A box contains 4 red and 3 blue identical balls. If two are picked at random, one after the other without replacement, find the probability that one is red and the other is blue.
-
A.
(frac{4}{7}) -
B.
(frac{2}{7}) -
C.
(frac{1}{7}) -
D.
(frac{1}{12})
Correct Answer: Option A
Explanation
P(one blue, other red) = P(1st red then blue) or P(1st blue then red)
= ((frac{4}{7} times frac{3}{6}) + (frac{3}{7} times frac{4}{6}))
= (frac{2}{7} + frac{2}{7} = frac{4}{7})