Two balls are drawn at random with replacement from a box containing 12 black and 9 red balls. Find the probability that first ball is black and second is red.
Answer & explanation
Correct answer: option 2
Black ball in bag = 12
total ball in bag = 21
probability that first ball is black =\(\frac{12}{21}\) =\(\frac{4}{7}\)
Ball has been replaced.
Now, red balls in bag = 9
total balls in bag = 21
probability that second ball is red = \(\frac{9}{21}\) =\(\frac{3}{7}\)
Probability of getting first ball black and second red = \(\frac{4}{7}\) × \(\frac{3}{7}\)
= \(\frac{12}{49}\)