Probability and p&c

Question

7 white balls and 3 black balls are placed in a row at random. The probability that no two black balls

are adjacent, is

(A) 2

(B) 7/15

(C) 2/15

(D) 13

Answer 1

Three black balls of 10 with gaps is 1-1 with three black balls of 8.

Thus, the probablility is P(8,3)/P(10,3) = 8*7*6/10*9*8 = 7*6/10*9 = 7/15

B