Question

There are 10 lamps in hall each of them can be switch on independently. The number of way in which hall can be lliuminated is.?

Answer 1

Given :

Total number of lamps =10

Since at least one lamp is to be kept switched on

The total number of ways are

10C1+10C2+....10C1010C1+10C2+....10C10

⇒210−1⇒210−1

⇒1024−1⇒1024−1

⇒1023

Answer 2

10c1 is the number of ways to illuminate the room.

because by switch on any of the lamp make room illuminated.

so answer will be 10C1