More Questions from Problems on H.C.F and L.C.M

Find the least number that must be added to 2497 so the resulting sum is exactly divisible by 5, 6, 4, and 3.

Aptitude Problems on H.C.F and L.C.M Difficulty: Easy
Choose an option
  • A
    3
  • B
    13
  • C
    23
  • D
    33
  • E
    17

Answer

Correct Answer: 23

Explanation

Introduction / Context:We are asked for the smallest nonnegative addition that makes a given number divisible by several integers at once. This is a classic application of least common multiple (LCM) and modular arithmetic.

Given Data / Assumptions:

  • Starting number: 2497
  • Divisors: 5, 6, 4, and 3
  • We want 2497 + x to be divisible by each divisor.

Concept / Approach:Compute LCM(5, 6, 4, 3). The sum must be a multiple of this LCM. Then find the smallest x such that 2497 + x ≡ 0 (mod LCM).

Step-by-Step Solution:LCM(5, 6, 4, 3) = LCM(5, 6) = 30; LCM(30, 4) = 60; LCM(60, 3) = 60.Compute remainder of 2497 modulo 60: 2497 = 60*41 + 37, so 2497 ≡ 37 (mod 60).We need x such that 37 + x ≡ 0 (mod 60) ⇒ x ≡ 23 (mod 60).Smallest nonnegative x is 23.

Verification / Alternative check:2497 + 23 = 2520. Dividing: 2520/5 = 504, /6 = 420, /4 = 630, /3 = 840. All are integers.

Why Other Options Are Wrong:3, 13, 33, and 17 do not make 2497 + x a multiple of 60; they leave nonzero remainders modulo 60.

Common Pitfalls:Taking LCM incorrectly (e.g., multiplying all divisors without reduction) or using the wrong remainder when computing x modulo the LCM.

Final Answer:23

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