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Question

9n + 7 is divisible by ________.


  1. 4

  2. 8

  3. 3

  4. 6


Solution

The correct options are
A

4


B

8


9n + 7 = (1+8)n+7

(1+8)n+7 = (nC0(8)n+nC1(8)n1+nC2(8)n2............+nCn1(8)1+nCn)+7

(1+8)n+7 = (nC0(8)n+nC1(8)n1+nC2(8)n2............+nCn1(8)1+1)+7

(1+8)n+7 = (nC0(8)n+nC1(8)n1+nC2(8)n2............+nCn1(8)1+8

              = 8k

It is divisible by 8 and 4

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