1 vote

Consider a sequence of 10 A's and 8 B's placed in a Row. By a run we mean one or more letters of the same type placed side by side. Here is a arrangement of 10 A's and 8 B's which contains 4 runs of A and 4 runs of B:

AAA BB A BBB AA B AAAA BB

In how many ways can 10 A's and 8 B's be arranged in a row so that there are 4 runs of A and 4 runs of B.

a) 2*(9c3)(7c3)

b) (9c3)(7c3)

c) (10c4)(8c4)

d) (10c5)(8c5)