In a box of 16 pens, a total of 3 are defective. If a customer buys 2 pens selected at random from the box, what is the probability that neither pen will be defective?
Select:
A) 1 / 6
B) 2 / 9
C) 6 / 20
D) 13 / 20
E) 3 / 4

Rationale: "method - 1 there are 9 fine pieces of pen and 3 defective in a lot of 16 pens i . e . probability of first pen not being defective = ( 13 / 16 ) i . e . probability of second pen not being defective = ( 12 / 15 ) [ 15 pen remaining with 12 defective remaining considering that first was defective ] probability of both pen being non - defective = ( 12 / 15 ) * ( 13 / 16 ) = 13 / 20 answer : option d"
Answer: D