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Question
There are 8 switches in a row from left to right on a switch board.At least one of the switches is switched on. In how many ways is this possible,if all the switches which are switched on are next to each other
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Answer
If only one switch is switched on, it can be done in 8 ways. If 2 switches are switched on, it can be done in 8-2+1 = 7 ways. Similarly for 3 switches, it will 8-3+1 = 6 ways. Thus, the answer is 8+7+6+5+4+3+2+1. Ans = 36
