Practise 62 selected previous-year MCQs with answers and compact worked solutions. Questions from 2023–2026 are labelled by Basic or Standard, examination, paper code and question number.
HCF & LCM QUESTION 1 · Easy · 1 MARK
CBSE 2023 · Standard · Main · 30/4/1 · Q1
Find the ratio of the HCF to the LCM of the least composite number and the least prime number. A. 1 : 2 B. 2 : 1 C. 1 : 1 D. 1 : 3
Show Answer & Explanation Least composite number = 4 Least prime number = 2 HCF(4, 2) = 2
LCM(4, 2) = 4
HCF : LCM = 2 : 4 = 1 : 2
Correct answer: A — 1 : 2
Common trap: 1 is neither prime nor composite.
Why the other choices are incorrect B reverses the ratio; C assumes the HCF equals the LCM; D gives an incorrect ratio.
Source: CBSE 2023 · Standard · Main · 30/4/1 · Q1 Wording lightly normalised. Solutions prepared by Team TutorVertex.
QUESTION 2 · Easy · 1 MARK
CBSE 2023 · Standard · Main · 30/2/1 · Q4
Natural numbers p and q satisfy: p is a multiple of q. What is their HCF? A. pq B. p C. q D. p + q
Show Answer & Explanation p is a multiple of q Therefore, q divides both p and q No factor of q can exceed q.
Hence, HCF(p, q) = q.
Correct answer: C — q
Common trap: When one number divides the other, their HCF is the smaller number.
Why the other choices are incorrect A is generally a multiple; B need not divide q; D exceeds both numbers.
Source: CBSE 2023 · Standard · Main · 30/2/1 · Q4 Wording lightly normalised. Solutions prepared by Team TutorVertex.
QUESTION 3 · Moderate · 1 MARK
CBSE 2024 · Standard · Main · 30/3/1 · Q5
If a = 2² × 3ˣ, b = 2² × 3 × 5 and c = 2² × 3 × 7, and LCM(a, b, c) = 3780, find x. A. 1 B. 2 C. 3 D. 0
Show Answer & Explanation a = 2² × 3ˣ b = 2² × 3 × 5 c = 2² × 3 × 7 LCM = 3780 3780 = 2² × 3³ × 5 × 7
LCM uses the greatest exponent of each prime.
Greatest exponent of 3 = 3
Hence, x = 3.
Correct answer: C — 3
Common trap: LCM takes the greatest exponent of each prime.
Why the other choices are incorrect A and D give LCM 420; B gives LCM 1260.
Source: CBSE 2024 · Standard · Main · 30/3/1 · Q5 Wording lightly normalised. Solutions prepared by Team TutorVertex.
QUESTION 4 · Moderate · 1 MARK
CBSE 2024 · Standard · Main · 30/4/1 · Q2
The HCF of 65 and 104 is 13. Their LCM is 40x. Find x. A. 5 B. 13 C. 40 D. 8
Show Answer & Explanation First number = 65 Second number = 104 HCF = 13 LCM = 40x HCF × LCM = Product of the numbers
13 × 40x = 65 × 104
520x = 6760
x = 6760 ÷ 520 = 13
Correct answer: B — 13
Common trap: After finding the LCM, divide by 40 to obtain x.
Why the other choices are incorrect A, C and D give LCM values 200, 1600 and 320, respectively; none equals 520.
Source: CBSE 2024 · Standard · Main · 30/4/1 · Q2 Wording lightly normalised. Solutions prepared by Team TutorVertex.
QUESTION 5 · Moderate · 1 MARK
CBSE 2024 · Standard · Main · 30/5/1 · Q13
Find the LCM of 28, 44 and 132. A. 258 B. 231 C. 462 D. 924
Show Answer & Explanation 28 = 2² × 7 44 = 2² × 11 132 = 2² × 3 × 11 LCM uses the greatest exponent of each prime.
LCM = 2² × 3 × 7 × 11
= 924
Correct answer: D — 924
Common trap: Take the largest prime powers across all three numbers.
Why the other choices are incorrect 258 is not divisible by 28; 231 and 462 lack the required factor 2².
Source: CBSE 2024 · Standard · Main · 30/5/1 · Q13 Wording lightly normalised. Solutions prepared by Team TutorVertex.
QUESTION 6 · Easy · 1 MARK
CBSE 2024 · Standard · Main · 30/5/1 · Q14
Two coprime numbers have product 553. What is their HCF? A. 1 B. 553 C. 7 D. 79
Show Answer & Explanation The numbers are coprime Their only common positive factor is 1 Therefore, HCF = 1.
Correct answer: A — 1
Common trap: Coprime does not mean both numbers must be prime.
Why the other choices are incorrect 553 is the product; 7 and 79 are factors of 553, not a common divisor of the coprime pair.
Source: CBSE 2024 · Standard · Main · 30/5/1 · Q14 Wording lightly normalised. Solutions prepared by Team TutorVertex.
QUESTION 7 · Moderate · 1 MARK
CBSE 2025 · Standard · Main · 30/1/1 · Q6
If HCF(98, 28) = m and LCM(98, 28) = n, find n − 7m. A. 0 B. 28 C. 98 D. 198
Show Answer & Explanation m = HCF = 2 × 7 = 14
n = LCM = 2² × 7² = 196
n − 7m = 196 − 7 × 14
= 196 − 98
= 98
Correct answer: C — 98
Common trap: Apply the subtraction after multiplying m by 7.
Why the other choices are incorrect A: 0 would require 7m = 196, but 7m = 98. B: 28 is a given number, not n − 7m. D: 198 is not the result of 196 − 98.
Source: CBSE 2025 · Standard · Main · 30/1/1 · Q6 Wording lightly normalised. Solutions prepared by Team TutorVertex.
QUESTION 8 · Easy · 1 MARK
CBSE 2025 · Standard · Main · 30/2/1 · Q10
Find the sum of the exponents in the prime factorisation of 4004. A. 5 B. 4 C. 3 D. 2
Show Answer & Explanation 4004 = 4 × 1001 = 2² × 7 × 11 × 13 Exponents: 2, 1, 1, 1
Sum = 2 + 1 + 1 + 1 = 5
Correct answer: A — 5
Common trap: A prime written without an exponent has exponent 1.
Why the other choices are incorrect B counts distinct primes; C and D omit some exponents.
Source: CBSE 2025 · Standard · Main · 30/2/1 · Q10 Wording lightly normalised. Solutions prepared by Team TutorVertex.
QUESTION 9 · Easy · 1 MARK
CBSE 2025 · Standard · Main · 30/2/1 · Q18
Find the HCF of 40, 110 and 360. A. 40 B. 110 C. 360 D. 10
Show Answer & Explanation 40 = 2³ × 5 110 = 2 × 5 × 11 360 = 2³ × 3² × 5 Common primes: 2 and 5
HCF uses their smallest exponents.
HCF = 2 × 5 = 10
Correct answer: D — 10
Common trap: A common divisor must divide every number in the list.
Why the other choices are incorrect 40 does not divide 110; 110 does not divide 40; 360 does not divide 40 or 110.
Source: CBSE 2025 · Standard · Main · 30/2/1 · Q18 Wording lightly normalised. Solutions prepared by Team TutorVertex.
QUESTION 10 · Moderate · 1 MARK
CBSE 2025 · Standard · Main · 30/3/1 · Q2
Let x = LCM(4, 6, 8), y = LCM(3, 5, 7), and p = LCM(x, y). Which statement is true? A. p = 35x B. p = 4y C. p = 8x D. p = 16y
Show Answer & Explanation x = LCM(4, 6, 8) y = LCM(3, 5, 7) x = 2³ × 3 = 24
y = 3 × 5 × 7 = 105
p = LCM(24, 105)
= 2³ × 3 × 5 × 7 = 840
35x = 35 × 24 = 840
Therefore, p = 35x.
Correct answer: A — p = 35x
Common trap: The second LCM uses the values of x and y, not the original lists.
Why the other choices are incorrect B gives 420; C gives 192; D gives 1680. The required value is 840.
Source: CBSE 2025 · Standard · Main · 30/3/1 · Q2 Wording lightly normalised. Solutions prepared by Team TutorVertex.
QUESTION 11 · Easy · 1 MARK
CBSE 2026 · Standard · Main · 30/1/1 · Q1
Find the HCF of 960 and 432. A. 48 B. 54 C. 72 D. 36
Show Answer & Explanation 960 = 2⁶ × 3 × 5 432 = 2⁴ × 3³ Common primes: 2 and 3
HCF uses their smallest exponents.
HCF = 2⁴ × 3 = 48
Correct answer: A — 48
Common trap: A candidate HCF must divide both numbers.
Why the other choices are incorrect 54, 72 and 36 do not divide 960.
Source: CBSE 2026 · Standard · Main · 30/1/1 · Q1 Wording lightly normalised. Solutions prepared by Team TutorVertex.
QUESTION 12 · Easy · 1 MARK
CBSE 2025 · Basic · Main · 430/1/1 · Q1
Two positive integers a and b have HCF 1. What is their LCM? A. a + b B. a C. b D. ab
Show Answer & Explanation HCF × LCM = a × b
1 × LCM = a × b
LCM = ab
Correct answer: D — ab
Common trap: HCF 1 means the two integers are coprime.
Why the other choices are incorrect A uses addition instead of multiplication. B and C are not general formulas for the LCM.
Source: CBSE 2025 · Basic · Main · 430/1/1 · Q1 Wording lightly normalised. Solutions prepared by Team TutorVertex.
QUESTION 13 · Moderate · 1 MARK
CBSE 2025 · Basic · Main · 430/3/1 · Q1
If p = 2³ × 3² × 5 and q = 2² × 3³, find LCM(p, q). A. 2³ × 3³ B. 2² × 3² C. 2² × 3² × 5 D. 2³ × 3³ × 5
Show Answer & Explanation p = 2³ × 3² × 5 q = 2² × 3³ Greatest exponent of 2 = 3
Greatest exponent of 3 = 3
Include the prime factor 5.
LCM(p, q) = 2³ × 3³ × 5
Correct answer: D — 2³ × 3³ × 5
Common trap: Keep the factor 5 even though it appears in only p.
Why the other choices are incorrect A omits 5; B uses smaller powers and omits 5; C uses smaller powers.
Source: CBSE 2025 · Basic · Main · 430/3/1 · Q1 Wording lightly normalised. Solutions prepared by Team TutorVertex.
QUESTION 14 · Moderate · 1 MARK
CBSE 2026 · Basic · Main · 430/4/1 · Q1
If HCF(850, 325) = 25, find LCM(850, 325). A. 442 B. 11050 C. 8450 D. 2210
Show Answer & Explanation First number = 850 Second number = 325 HCF = 25 HCF × LCM = Product of the numbers
25 × LCM = 850 × 325
LCM = (850 × 325) ÷ 25
= 850 × 13
= 11050
Correct answer: B — 11050
Common trap: Divide the product by the HCF, rather than by one of the numbers.
Why the other choices are incorrect 442, 8450 and 2210 are not common multiples of both 850 and 325.
Source: CBSE 2026 · Basic · Main · 430/4/1 · Q1 Wording lightly normalised. Solutions prepared by Team TutorVertex.
QUESTION 15 · Easy · 1 MARK
CBSE 2026 · Basic · Main · 430/4/2 · Q9
Find the HCF of two consecutive natural numbers. A. 2 B. 1 C. 0 D. the smaller number
Show Answer & Explanation Difference between consecutive natural numbers = 1 A common factor must divide their difference.
The only positive factor of 1 is 1.
Therefore, HCF = 1.
Correct answer: B — 1
Common trap: Consecutive numbers are always coprime.
Why the other choices are incorrect A fails for 2 and 3; C cannot be the HCF of positive integers; D is not true in general.
Source: CBSE 2026 · Basic · Main · 430/4/2 · Q9 Wording lightly normalised. Solutions prepared by Team TutorVertex.
QUESTION 16 · Easy · 1 MARK
CBSE 2023 · Basic · Main · 430/2/1 · Q7
If HCF(360, 64) = 8, find their LCM. A. 2480 B. 2780 C. 512 D. 2880
Show Answer & Explanation Numbers: 360 and 64 HCF = 8 HCF × LCM = 360 × 64
LCM = (360 × 64) ÷ 8
= 360 × 8 = 2880
Correct answer: D — 2880
Common trap: Divide the product by the HCF.
Source: CBSE 2023 · Basic · Main · 430/2/1 · Q7 Wording lightly normalised. Solutions prepared by Team TutorVertex.
QUESTION 17 · Easy · 1 MARK
CBSE 2023 · Basic · Main · 430/2/2 · Q13
If HCF(72, 234) = 18, find LCM(72, 234). A. 936 B. 836 C. 324 D. 234
Show Answer & Explanation Numbers: 72 and 234 HCF = 18 LCM = (72 × 234) ÷ 18
= 4 × 234
= 936
Correct answer: A — 936
Common trap: Use both numbers in the product.
Source: CBSE 2023 · Basic · Main · 430/2/2 · Q13 Wording lightly normalised. Solutions prepared by Team TutorVertex.
QUESTION 18 · Easy · 1 MARK
CBSE 2023 · Basic · Main · 430/4/1 · Q2
Find HCF × LCM for the numbers 70 and 40. A. 10 B. 280 C. 2800 D. 70
Show Answer & Explanation HCF × LCM = Product of the two numbers
= 70 × 40
= 2800
Correct answer: C — 2800
Common trap: The question asks for the product, not the HCF alone.
Source: CBSE 2023 · Basic · Main · 430/4/1 · Q2 Wording lightly normalised. Solutions prepared by Team TutorVertex.
QUESTION 19 · Easy · 1 MARK
CBSE 2023 · Basic · Main · 430/4/2 · Q8
Find HCF × LCM for the numbers 30 and 70. A. 2100 B. 21 C. 210 D. 70
Show Answer & Explanation QUESTION 20 · Easy · 1 MARK
CBSE 2023 · Basic · Main · accessible paper · 430(B) · Q1
If x = a³b² and y = ab³, where a and b are prime factors, find HCF(x, y). A. ab B. ab² C. a³b³ D. a²b²
Show Answer & Explanation QUESTION 21 · Easy · 1 MARK
CBSE 2023 · Basic · Main · accessible paper · 430(B) · Q2
Find the product of the HCF and LCM of 50 and 20. A. 10 B. 100 C. 1000 D. 20
Show Answer & Explanation QUESTION 22 · Easy · 1 MARK
CBSE 2023 · Basic · Supplementary · 430/C/3 · Q4
Two numbers have HCF 27 and LCM 162. If one number is 54, find the other. A. 36 B. 45 C. 9 D. 81
Show Answer & Explanation HCF = 27 LCM = 162 First number = 54 Product of numbers = 27 × 162
Other number = (27 × 162) ÷ 54
= 81
Correct answer: D — 81
Common trap: Check: HCF(54, 81) = 27 and LCM = 162.
Source: CBSE 2023 · Basic · Supplementary · 430/C/3 · Q4 Wording lightly normalised. Solutions prepared by Team TutorVertex.
QUESTION 23 · Easy · 1 MARK
CBSE 2024 · Standard · Main · accessible paper · 30(B) · Q1
Find the LCM of 24, 36 and 60 in prime-factor form. A. 2² × 3 × 5 B. 2³ × 3² C. 2³ × 3² × 5 D. 2³ × 3³ × 5
Show Answer & Explanation QUESTION 24 · Easy · 1 MARK
CBSE 2024 · Standard · Main · 30/5/3 · Q1
Find the LCM of the smallest prime number and the smallest odd composite number. A. 10 B. 6 C. 9 D. 18
Show Answer & Explanation Smallest prime = 2 Smallest odd composite = 9 2 and 9 have no common prime factor.
LCM = 2 × 9 = 18
Correct answer: D — 18
Common trap: 1 is not composite; 3, 5 and 7 are prime.
Source: CBSE 2024 · Standard · Main · 30/5/3 · Q1 Wording lightly normalised. Solutions prepared by Team TutorVertex.
QUESTION 25 · Easy · 1 MARK
CBSE 2024 · Basic · Main · 430/2/1 · Q1
Find the HCF of the smallest two-digit number and the smallest composite number. A. 2 B. 20 C. 40 D. 4
Show Answer & Explanation Smallest two-digit number = 10 Smallest composite number = 4 10 = 2 × 5; 4 = 2²
HCF = 2
Correct answer: A — 2
Common trap: The smallest composite number is 4, not 1.
Source: CBSE 2024 · Basic · Main · 430/2/1 · Q1 Wording lightly normalised. Solutions prepared by Team TutorVertex.
QUESTION 26 · Easy · 1 MARK
CBSE 2024 · Basic · Main · 430/5/1 · Q1
Find HCF × LCM for the numbers 40 and 30. A. 12 B. 120 C. 1200 D. 40
Show Answer & Explanation QUESTION 27 · Easy · 1 MARK
CBSE 2024 · Basic · Supplementary · 430/S/1 · Q1
If a = 2⁷ × 3¹⁰ and b = 2³ × 3⁷, find HCF(a, b). A. 2⁷ × 3¹⁰ B. 2¹⁰ × 3¹⁷ C. 2³ × 3⁷ D. 2⁷ × 3⁷
Show Answer & Explanation QUESTION 28 · Easy · 1 MARK
CBSE 2024 · Basic · Supplementary · 430/S/1 · Q12
Find the LCM of the smallest odd prime number and the greatest two-digit number. A. 1 B. 99 C. 297 D. 300
Show Answer & Explanation Smallest odd prime = 3 Greatest two-digit number = 99 99 is already divisible by 3.
LCM(3, 99) = 99.
Correct answer: B — 99
Common trap: When one number divides the other, LCM is the larger number.
Source: CBSE 2024 · Basic · Supplementary · 430/S/1 · Q12 Wording lightly normalised. Solutions prepared by Team TutorVertex.
QUESTION 29 · Easy · 1 MARK
CBSE 2024 · Standard · Supplementary · 30/S/1 · Q2
If m = p⁵q² and n = p³q⁴, where p and q are prime factors, find LCM(m, n). A. p⁸q⁶ B. p³q² C. p⁵q⁴ D. p⁵q² + p³q⁴
Show Answer & Explanation Exponents of p: 5 and 3 Exponents of q: 2 and 4 Take the greater exponent of each prime.
LCM = p⁵q⁴.
Correct answer: C — p⁵q⁴
Common trap: Do not add exponents; that gives the product rather than the LCM.
Source: CBSE 2024 · Standard · Supplementary · 30/S/1 · Q2 Wording lightly normalised. Solutions prepared by Team TutorVertex.
QUESTION 30 · Easy · 1 MARK
CBSE 2025 · Standard · Main · accessible paper · 30(B) · Q1
Find the HCF and LCM, respectively, of 14, 21 and 77. A. 7, 77 B. 14, 462 C. 7, 462 D. 21, 77
Show Answer & Explanation 14 = 2 × 7 21 = 3 × 7 77 = 7 × 11 Common prime = 7, so HCF = 7
LCM = 2 × 3 × 7 × 11 = 462
Correct answer: C — 7, 462
Common trap: The HCF–LCM product rule for two numbers must not be extended to three numbers.
Source: CBSE 2025 · Standard · Main · accessible paper · 30(B) · Q1 Wording lightly normalised. Solutions prepared by Team TutorVertex.
QUESTION 31 · Easy · 1 MARK
CBSE 2025 · Basic · Main · 430/2/1 · Q1
Find HCF − LCM for the numbers 3 and 5. A. 2 B. 4 C. 14 D. −14
Show Answer & Explanation HCF(3, 5) = 1 LCM(3, 5) = 15 HCF − LCM = 1 − 15
= −14
Correct answer: D — −14
Common trap: Keep the subtraction in the order given.
Source: CBSE 2025 · Basic · Main · 430/2/1 · Q1 Wording lightly normalised. Solutions prepared by Team TutorVertex.
QUESTION 32 · Easy · 1 MARK
CBSE 2025 · Basic · Supplementary · accessible paper · 430(B)/S · Q2
If p = ab²c³ and q = a²b³c², where a, b and c are prime factors, find LCM(p, q). A. ab²c² B. a²b³c³ C. a²b²c² D. abc
Show Answer & Explanation QUESTION 33 · Moderate · 1 MARK
CBSE 2025 · Basic · Supplementary · accessible paper · 430(B)/S · Q1
Find the greatest speed at which a person can cover 78 m and 104 m in an exact whole number of minutes each. A. 17 m/min B. 13 m/min C. 26 m/min D. 39 m/min
Show Answer & Explanation QUESTION 34 · Easy · 1 MARK
CBSE 2025 · Standard · Supplementary · accessible paper · 30(B)/S · Q1
Find the ratio of the HCF to the LCM of 7, 21 and 28. A. 1 : 4 B. 3 : 4 C. 1 : 8 D. 1 : 12
Show Answer & Explanation QUESTION 35 · Easy · 1 MARK
CBSE 2026 · Standard · Main · accessible paper · 30(B) · Q17
If HCF(66, 99) = 55m − 132, find m. A. 4 B. 2 C. 1 D. 3
Show Answer & Explanation QUESTION 36 · Easy · 1 MARK
CBSE 2026 · Standard · Main · 30/2/3 · Q6
Find the LCM of 960 and 240. A. 960 B. 240 C. 60 D. 15
Show Answer & Explanation 960 is a multiple of both numbers.
No smaller positive multiple of 960 exists.
Therefore, LCM = 960.
Correct answer: A — 960
Common trap: When one number divides the other, LCM is the larger number.
Source: CBSE 2026 · Standard · Main · 30/2/3 · Q6 Wording lightly normalised. Solutions prepared by Team TutorVertex.
QUESTION 37 · Easy · 1 MARK
CBSE 2026 · Basic · Second examination · accessible paper · 430(B) · Q1
If HCF(p, 8) = 4 and LCM(p, 8) = 24, find p. A. 8 B. 3 C. 12 D. 18
Show Answer & Explanation QUESTION 38 · Easy · 1 MARK
CBSE 2026 · Standard · Second examination · 30/7/1 · Q1
For two positive integers a and b, which relationship is always true? A. HCF(a, b) + LCM(a, b) = a + b B. HCF(a, b) + LCM(a, b) = a × b C. HCF(a, b) × LCM(a, b) = a × b D. HCF(a, b) = LCM(a, b)
Show Answer & Explanation QUESTION 39 · Easy · 1 MARK
CBSE 2026 · Standard · Second examination · 30/7/1 · Q3
If a = x³y² and b = xy³, where x and y are prime factors, find LCM(a, b). A. xy B. xy² C. x³y³ D. x²y²
Show Answer & Explanation QUESTION 40 · Easy · 1 MARK
CBSE 2026 · Standard · Second examination · 30/7/2 · Q14
Find the least positive integer divisible by every natural number from 1 to 10 inclusive. A. 10 B. 100 C. 504 D. 2520
Show Answer & Explanation Required number = LCM(1, 2, …, 10) Greatest prime powers needed: 2³, 3², 5 and 7
LCM = 2³ × 3² × 5 × 7
= 2520
Correct answer: D — 2520
Common trap: 504 is not divisible by 5, so it cannot be the required number.
Source: CBSE 2026 · Standard · Second examination · 30/7/2 · Q14 Wording lightly normalised. Solutions prepared by Team TutorVertex.
Irrational numbers QUESTION 56 · Moderate · 1 MARK
CBSE 2024 · Standard · Main · 30/3/1 · Q14
Which pair consists of irrational numbers with a rational product? A. (√16, √4) B. (√5, √2) C. (√3, √27) D. (√36, √2)
Show Answer & Explanation √3 is irrational √27 = 3√3 is irrational √3 × √27 = √81 = 9
9 is rational.
Required pair: (√3, √27).
Correct answer: C — (√3, √27)
Common trap: Both numbers must be irrational, as well as their product being rational.
Why the other choices are incorrect A contains two rational numbers; B has product √10; D contains the rational number 6.
Source: CBSE 2024 · Standard · Main · 30/3/1 · Q14 Wording lightly normalised. Solutions prepared by Team TutorVertex.
QUESTION 57 · Easy · 1 MARK
CBSE 2025 · Basic · Main · 430/1/1 · Q2
The number 3 + √2 is: A. a rational number B. an irrational number C. an integer D. a natural number
Show Answer & Explanation √2 is irrational Suppose 3 + √2 is rational √2 = (3 + √2) − 3
This would make √2 rational: a contradiction.
Therefore, 3 + √2 is irrational.
Correct answer: B — an irrational number
Common trap: Adding a rational number does not remove an irrational part.
Why the other choices are incorrect A contradicts the argument; integers and natural numbers are rational, ruling out C and D.
Source: CBSE 2025 · Basic · Main · 430/1/1 · Q2 Wording lightly normalised. Solutions prepared by Team TutorVertex.
QUESTION 58 · Easy · 1 MARK
CBSE 2023 · Basic · Main · accessible paper · 430(B) · Q3
The product of a non-zero rational number and an irrational number is: A. always irrational B. always rational C. rational or irrational D. always positive
Show Answer & Explanation r is rational and r ≠ 0 x is irrational Suppose rx is rational.
Then x = (rx) ÷ r would be rational.
This is a contradiction. Hence rx is irrational.
Correct answer: A — always irrational
Common trap: The rational multiplier must be non-zero.
Source: CBSE 2023 · Basic · Main · accessible paper · 430(B) · Q3 Wording lightly normalised. Solutions prepared by Team TutorVertex.
QUESTION 59 · Moderate · 1 MARK
CBSE 2025 · Standard · Main · 30/5/1 · Q1
(√3 + 2)² + (√3 − 2)² is a/an: A. positive rational number B. negative rational number C. positive irrational number D. negative irrational number
Show Answer & Explanation Use (a + b)² + (a − b)² = 2a² + 2b². (√3 + 2)² + (√3 − 2)² = 2 × 3 + 2 × 4
= 6 + 8 = 14
14 is positive and rational.
Correct answer: A — positive rational number
Common trap: The opposite surd terms cancel when the squares are added.
Why the other choices are incorrect B: 14 is positive. C and D: the surd terms cancel, leaving the integer 14.
Source: CBSE 2025 · Standard · Main · 30/5/1 · Q1 Wording lightly normalised. Solutions prepared by Team TutorVertex.
QUESTION 60 · Moderate · 1 MARK
CBSE 2025 · Basic · Main · 430/5/1 · Q1
(2 − 5√3)² is: A. a negative integer B. an irrational number C. a rational number D. a positive integer
Show Answer & Explanation Use (a − b)² = a² − 2ab + b². (2 − 5√3)² = 4 − 20√3 + 75
= 79 − 20√3
20√3 is irrational; subtracting it from 79 gives an irrational number.
Correct answer: B — an irrational number
Common trap: Squaring an irrational expression does not always give a rational number.
Why the other choices are incorrect A and D: integers are rational, but this expression is irrational. C: the non-zero √3 term remains.
Source: CBSE 2025 · Basic · Main · 430/5/1 · Q1 Wording lightly normalised. Solutions prepared by Team TutorVertex.
QUESTION 61 · Moderate · 1 MARK
CBSE 2025 · Basic · Main · 430/5/3 · Q18
√2(√2 − 1) is: A. an integer B. a rational number C. an irrational number D. equal to 1
Show Answer & Explanation √2(√2 − 1) = 2 − √2
If 2 − √2 were rational, then √2 = 2 − (2 − √2) would be rational.
This is a contradiction, so the expression is irrational.
Correct answer: C — an irrational number
Common trap: Multiply √2 by both terms inside the brackets.
Why the other choices are incorrect A and B: 2 − √2 is irrational, so it cannot be an integer or rational. D: equality to 1 would require √2 = 1.
Source: CBSE 2025 · Basic · Main · 430/5/3 · Q18 Wording lightly normalised. Solutions prepared by Team TutorVertex.
QUESTION 62 · Moderate · 1 MARK
CBSE 2026 · Basic · Second examination · 430/8/1 · Q14
Which pair of irrational numbers has a rational product? A. (√8, √32) B. (√3, √5) C. (√8, √20) D. (√2, √15)
Show Answer & Explanation √8 and √32 are both irrational. √8 × √32 = √256 = 16
16 is rational.
Correct answer: A — (√8, √32)
Common trap: Two irrational factors can have a rational product.
Why the other choices are incorrect B: √15 is irrational. C: √160 = 4√10 is irrational. D: √30 is irrational.
Source: CBSE 2026 · Basic · Second examination · 430/8/1 · Q14 Wording lightly normalised. Solutions prepared by Team TutorVertex.