A bag contains 3 red marbles, 2 blue marbles and 4 green marbles. Each color type has a distinguishing feature. If 3 marbles are chosen randomly, how many ways can you select at most 1 red marbles.
Case 1: You pick no red marbles... to get that you would have to pick either green or blue marbles only. So there would be 6x5x4=120 ways.
Case 2: You pick only 1 red marble. There are 3 ways to pick a red marble and then 6x5 more ways to choose a green or blue marble, so 6x5x3=90 ways.
So you add up both cases and get 120+90=210 ways.