How many ways can 2 identical red chairs and 4 identical blue chairs be arranged in one row ?

Options

A. 6
B. 15
C. 21
D. 24

Answer

B

Explanation

There is a formula that applies to this situation. The number of distinct permutations of n things, a of which are indistinguishable, b of which are indistinguishable, atc., is
`(n!)/(a!b!...)`
Here there are 6 chairs, 2 of which are indistinguishable and 4 of which are indistinguishable, so the number of permutations is
`(6!)/(2!4!)=(6.5.4.3.2.1)/(2.1.4.3.2.1)=(6.5)/(2)=15`