A box contains 21 electric bulbs, out of which 4 are defective. Two bulbs are chosen at random from this box. The probability that at least one of these is defective is  Choose the correct option:
A) 4/19
B) 7/19
C) 12/19
D) 21/95
E) 31/88
Solution   P( None is defective)   = 17C2 / 21C2   = 57/88.   P( at least one is defective)   = (1- 57/88)   = 31/88.   Answer 31/88
<result>E</result>
A box contains 21 electric bulbs, out of which 4 are defective. Two bulbs are chosen at random from this box. The probability that at least one of these is defective is