Question

A box contains S defective and 15 non defective bulbs. Two bulbs are chosen at random. Find the probability that both the bulbs are non- defective.

Answer 1

Total = 5 + 15 = 20, 

n(S) = 20c₂ = \(\frac{20\times19}{2\times1} = 190\)

Let A = both bulbs are non-defective 

n(A)= 15c₂= \(\frac{14\times15}{2\times 1} = 105\)

P(A) = \(\frac{n(A)}{n(S)}\) = \(\frac{105}{190}\) = \(\frac{21}{38}\)