There are 3 red and 9 blue counters in a box. A counter is chosen and then replaced. If you did this 144 times, how many times would you expect to get a blue?

If you do it 144 times that is (3+9) * 12

This means that 12 times 3 red and 9 blue counters will be chosen that means that 9 blue counters will be chosen 12 times. 9*12 is 108.

This means blue counters will be chosen 108 times.

This can be checked as 108/3 would give you the number of red counters which is 36 and 108+36 is 144