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    Question

    What is the greatest four-digit number that leaves

    remainders 1, 2 and 3 respectively when divided by 2, 3 and 4?
    A 9995 Correct Answer Incorrect Answer
    B 9991 Correct Answer Incorrect Answer
    C 9993 Correct Answer Incorrect Answer
    D 9997 Correct Answer Incorrect Answer

    Solution

    ATQ, Let the required number be N. Given: N ≡ 1 (mod 2) N ≡ 2 (mod 3) N ≡ 3 (mod 4) Note that these remainders are each one less than the divisor: N ≡ −1 (mod 2), (mod 3), (mod 4) ⇒ N + 1 is divisible by 2, 3 and 4. So N + 1 is a multiple of LCM(2,3,4) = 12. Let N + 1 = 12k. For largest 4-digit N: N ≤ 9999 ⇒ 12k − 1 ≤ 9999 ⇒ 12k ≤ 10000 ⇒ k ≤ 833. Max k = 833 ⇒ N = 12 × 833 − 1 = 9996 − 1 = 9995.

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