Hello, digitalis77!

This is a tricky (but immensely satisfying) problem.

First, select the 5 rooms to be blue and the 2 to be green..The 7 rooms of a new home are to be painted.

Each room is to be painted one color from a selection of:

. . 4 shades of blue (B1,B2,B3,B4),

. . 3 shades of green (G1,G2,G3),

. . 2 shades of red (R1,R2).

More than one room may have the same color.

Count the number of ways each of the following steps can be completed

to determine the number of different ways to paint the 7 rooms.

a) If 5 are to be painted a shade of blue and 2 a shade of green.

. . There are: . choices.

For each of the 5 blue rooms, there are 4 choices of blue.

. . There are: . choices.

For each of 2 green rooms, there are 3 choices of green.

. . There are: . choices.

Therefore, there arte: .

b) 3 rooms some shade of red, 3 rooms some shade of blue

and one room some shade of green.

How many different ways can the seven rooms be painted?

First, select the 3 rooms to be red, 3 rooms to be blue, and 1 to be green.

. . There are: . choices.

For each of the 3 red rooms, there are 2 choices of red.

. . There are: . choices.

For each of 3 blue rooms, there are 4 choices of blue.

. . There are: . choices.

For the one green room, there are 3 choices of green: . choices.

Therefore, there are: .

For each of the seven rooms, there are nine choices of colors.c) How many ways can the rooms be painted?

. . There are: .

For each of the 7 rooms, there is a choice of 2 reds.d) How many different ways can all the rooms be painted red?

. . There are: .

The opposite of "at least one green or blue" is "e) How many different ways can the rooms be painted

if at least one room is green or blue?nogreen or blue" ... all red.

From part (c), there are: . ways to paint the rooms

. . of which (d) 128 ways areall red.

Therefore, there are: .

. . in which there is at least one green or one blue.