Problem number 21. Adam and Brenda have nine marbles each. Together they have eight red and ten blue marbles. Brenda has twice as many blue marbles as red marbles. How many blue marbles does Adam have? Let's break this problem down into steps and let's notice that the order in which the information is given isn't necessarily the order in which we're going to be using it. We do know that each person has nine marbles and we know that Brenda has twice as many blue marbles as red marbles. That means that for however many red marbles she has, she has two such groups of blue marbles, which means that we can divide all her marbles into three groups. Since she has nine marbles total, each of the groups is going to be three marbles because three plus three plus three is nine. She has three red marbles and six blue marbles. Now we we know how many blue marbles there are all together, ten, and we want to find out how many blue marbles Adam has. If Brenda has six blue marbles, then Adam will have the remaining blue marbles. Ten minus six is four. The answer is B, four.

marbles

Adam

Brenda

blue

red