Q9: In his pocket, a boy has 3 red marbles, 4 blue marbles, and 4 green
marbles. How many will he have to take out of his pocket to ensure
that he has taken out at least one of each color?
Well if the first 3 the took were red and the next 4 he took were blue, that would be seven, so the next one would have to be green and he would then have one of each colour.
But if he took 4 blue then 4 green the next one would be red and that would make 9.
The idea here is to add the 2 biggest numbers so there is no chance you can miss a colour.