Question

A box contains four 40-W bulbs, five 60-W
bulbs, and six 75-W bulbs. If bulbs are se-
lected one by one in random order, what is
the probability that at least two bulbs must be
selected to obtain one that is rated 75W?

Answer 1

so first one is not a 75W bulb:
P(not a 75Wbulb)=(4+5)/(4+5+6)=9/15
P(a 75W bulb)=6/(15-1)=6/14
9/15*6/14=9/35