Disciplined Boy/Girl

Assume that you're late for the school and when you reached there, you found that all of your 20 classmates are standing in a row. Then you have to occupy a position in that row, how many options are there for you?

Clarification: There is exactly one position vacant in front of and behind your each classmate.

18 19 21 20

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1 solution

Zee Ell
Aug 17, 2016

You can stand either in the front of the row (1 position) or behind each of your 20 classmates (20 positions).

Therefore, you have 20 + 1 = 21 options altogether.

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