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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 ≑ βˆ’1 (mod 2), (mod 3), (mod 4) β‡’ 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 β‡’ 12k βˆ’ 1 ≀ 9999 β‡’ 12k ≀ 10000 β‡’ k ≀ 833. Max k = 833 β‡’ N = 12 Γ— 833 βˆ’ 1 = 9996 βˆ’ 1 = 9995.

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