In a row of five squares, each square is to be colored either red, yellow, or blue, so that no two consecutive squares have the same color, and at lest three of the squares are red. How many ways are there to color the five squares?
if at least 3 of them are red... then they have to be positioned like this so that they don't touch:
red ? red ? red
now for the first question mark there are 2 choices, same for the second one. so our answer is 2x2 which is 4