NDA NA — Quantitative Aptitude: Number System

Practice these 20 carefully selected MCQs on Number System for NDA NA 2026. Each question includes the correct answer and a clear explanation. Practising MCQs regularly is the best way to improve speed and accuracy.

Instructions

  • Attempt all questions without looking at answers first.
  • Time yourself: target 1 minute per question.
  • Review explanations for every wrong answer.

Q1. What is the LCM of 12 and 18?

  • A. 36
  • B. 24
  • C. 72
  • D. 18
Answer: A — LCM(12,18) = 36.

Q2. HCF of 48 and 72?

  • A. 24
  • B. 12
  • C. 36
  • D. 48
Answer: A — 48=2⁴×3, 72=2³×3². HCF=2³×3=24.

Q3. Which is a prime number?

  • A. 37
  • B. 39
  • C. 35
  • D. 33
Answer: A — 37 is prime. Others divisible by 3 or 5.

Q4. What is the value of 2⁸?

  • A. 256
  • B. 128
  • C. 512
  • D. 64
Answer: A — 2⁸=256.

Q5. Sum of first 10 natural numbers?

  • A. 55
  • B. 50
  • C. 45
  • D. 60
Answer: A — n(n+1)/2 = 10×11/2 = 55.

Q6. What is 15% of 200?

  • A. 30
  • B. 25
  • C. 35
  • D. 20
Answer: A — 15/100×200=30.

Q7. √144 = ?

  • A. 12
  • B. 11
  • C. 13
  • D. 14
Answer: A — 12²=144.

Q8. 3³ + 4² = ?

  • A. 43
  • B. 37
  • C. 41
  • D. 45
Answer: A — 27+16=43.

Q9. Which is not a factor of 36?

  • A. 8
  • B. 6
  • C. 9
  • D. 12
Answer: A — 36=4×9=6²=3×12. 8 is not a factor.

Q10. LCM of 5, 6, 9?

  • A. 90
  • B. 45
  • C. 30
  • D. 60
Answer: A — LCM(5,6,9)=90.

Q11. The number 561 is divisible by:

  • A. 3
  • B. 7
  • C. 11
  • D. Both A and C
Answer: D — 5+6+1=12 (div by 3). 5-6+1=0 (div by 11). So both 3 and 11.

Q12. Find the remainder when 29 is divided by 7.

  • A. 1
  • B. 2
  • C. 3
  • D. 4
Answer: A — 29=4×7+1. Remainder=1.

Q13. What is the GCF/HCF of 60 and 84?

  • A. 12
  • B. 6
  • C. 24
  • D. 18
Answer: A — 60=2²×3×5, 84=2²×3×7. HCF=2²×3=12.

Q14. Which of the following is even?

  • A. 8
  • B. 7
  • C. 11
  • D. 13
Answer: A — 8 is even.

Q15. The number of prime numbers between 20 and 40?

  • A. 4
  • B. 5
  • C. 3
  • D. 6
Answer: A — Primes: 23,29,31,37 = 4 primes.

Q16. What is the smallest 4-digit number divisible by 9?

  • A. 1008
  • B. 1000
  • C. 1001
  • D. 1017
Answer: A — 1008/9=112. Yes, divisible.

Q17. The product of two numbers is 120. Their HCF is 6. LCM is?

  • A. 20
  • B. 30
  • C. 24
  • D. 40
Answer: A — LCM = Product/HCF = 120/6=20.

Q18. 2 × 2 × 2 × 2 × 2 = ?

  • A. 32
  • B. 16
  • C. 64
  • D. 8
Answer: A — 2⁵=32.

Q19. The cube of 5 is?

  • A. 125
  • B. 25
  • C. 625
  • D. 75
Answer: A — 5³=125.

Q20. What is the successor of 9999?

  • A. 10000
  • B. 9998
  • C. 10001
  • D. 9999
Answer: A — Successor = next number = 10000.

Exam Tips for Number System

  • Regular practice of 20+ questions daily builds speed and accuracy.
  • Review your mistakes — understanding why you got it wrong is crucial.
  • Attempt this topic in full mock tests under timed conditions.