Railway Exams (RRB) · Mathematics

Number System & Simplification

15 practice questions with full step-by-step solutions, plus a concept-first explainer — free, no sign-up.

Read the explainer · 7 minPractise · 15 questions

What you'll learn

Learn to sort numbers by type, apply divisibility shortcuts, crack LCM and HCF, and simplify with BODMAS — the fast, low-effort marks that lift your RRB NTPC maths score.

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8
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Number System & Simplification — solved practice questions

8 Railways Mathematics questions with step-by-step solutions. Attempt each, then reveal the answer.

  1. Q1easy

    What is the LCM of 12, 15 and 20?

    • A30
    • B45
    • C60
    • D120
    Show answer & solution

    Correct answer: (C) 60

    12 = 2^2*3, 15 = 3*5, 20 = 2^2*5. Taking the highest powers: 2^2*3*5 = 60.

  2. Q2easy

    What is the HCF (GCD) of 36 and 48?

    • A6
    • B12
    • C18
    • D24
    Show answer & solution

    Correct answer: (B) 12

    36 = 2^2*3^2 and 48 = 2^4*3. Common factors give HCF = 2^2*3 = 12.

  3. Q3easy

    Simplify: 15 + 3 × 4 − 6 ÷ 2

    • A24
    • B30
    • C21
    • D27
    Show answer & solution

    Correct answer: (A) 24

    By BODMAS, do ÷ and × first: 6÷2 = 3 and 3×4 = 12, so 15 + 12 − 3 = 24.

  4. Q4easy

    What is the sum of the first 50 natural numbers?

    • A1250
    • B2550
    • C1225
    • D1275
    Show answer & solution

    Correct answer: (D) 1275

    Sum = n(n+1)/2 = 50 × 51 / 2 = 1275.

  5. Q5medium

    What is the sum of the first 20 even numbers (2 + 4 + ... + 40)?

    • A400
    • B420
    • C410
    • D440
    Show answer & solution

    Correct answer: (B) 420

    Sum of first n even numbers = n(n+1) = 20 × 21 = 420.

  6. Q6medium

    What is the unit (last) digit of 3^24?

    • A1
    • B3
    • C7
    • D9
    Show answer & solution

    Correct answer: (A) 1

    The unit digit of powers of 3 cycles 3, 9, 7, 1 with period 4. Since 24 is a multiple of 4, the unit digit is 1.

  7. Q7medium

    What is the square root of 5184?

    • A68
    • B74
    • C72
    • D76
    Show answer & solution

    Correct answer: (C) 72

    72 × 72 = 5184, so the square root of 5184 is 72.

  8. Q8medium

    What is the sum of the first 12 odd numbers (1 + 3 + ... + 23)?

    • A120
    • B132
    • C156
    • D144
    Show answer & solution

    Correct answer: (D) 144

    The sum of the first n odd numbers equals n^2, so 12^2 = 144.

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