UGC NET Paper 1 GA 2011 Dec Solved Paper

Question : 20 of 60

Marks: +1, -0

There are 10 lamps in a hall. Each one of them can be switched on independently. The number of ways in which hall can be illuminated is

Solution:

Since at least one lamp is to be kept Switched on. The total no. of ways

= ^10C_1 + ^10C_2........+ ^10C_10

= 210 -1

= 1024 - 1 = 1023

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