A box contains 10 bulbs,of which just three are defective. If a random sample of five bulbs is drawn, find the probability that the sample contains exactly one defective bulb.

Total number of elementary events =  $10C5$

Number of ways of selecting exactly one defective bulb out of 3 and 4 non-defective out of 7 is  $3C1*7C4$

So,required probability = $3C1*7C4$/ $10C5$ = 5/12.