There are three lamps in a hall. If each lamp can be switched on and off independently, in how many ways can the hall be illuminated? (The hall is illuminated when at least one of the lamps is on.)
I do not understand the OE. Can some one explain this pls?
As each lamp can be in either of the two modes (ON/OFF), there are 2*2*2=8 possibilities. But as the stem says, the possibility when all the lamps are off does not count. Therefore the answer is 7.
there are only 2 option s = on/off = 2ways
now if u try this on 3lamps = 2^3 ways = 8 ways
on on on
on on off
on off off........................... this is not valid ( atleast one should be on)
on off on
off off off
off on on
off off on
off on off