Seven different models cars, from which there are three blue and four red, are to be parked in a row. Find how many different arrangements there are if no two cars of the same color are to be parked next to each other.

Answer 1

A blue car cannot be on either end.
So we have to start and end with a red car.
They must be parked this way

RBRBRBR

number of way to do this is
R-B-R-B-R-B-R
4x3x3x2x2x1x1
= 144