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Question

From a collection of 20 consecutive natural numbers, four are selected such that they are not consecutive. The number of such selections is 
  1. 284×17
  2. 285×17
  3. 284×16
  4. 285×16


Solution

The correct option is A 284×17
1,2,3,4,.....,20
There are 17 way for four consecutive number.

Number of selections = 20C417
                                   =285×1717
                                   =284×17

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