  ### Home > MC1 > Chapter 5 > Lesson 5.2.1 > Problem5-40

5-40.

A bag of marbles contains only the colors red and green.

1. If the probability of getting a red marble is $\frac { 1 } { 3 }$, what is the probability of getting a green marble?

The probability stated means that if there are $3$ marbles in the bag, there is only one chance that you will pull out a red marble. How many chances are there that you will pull out a green marble?

If there were only three marbles in the bag, and one of them is red, then the other $2$ must be green. This means that $2$ out of $3$ marbles are green, so the probability must be $\frac{2}{3}.$

Another way to think of this is that if $1$ of every $3$ marbles is red, then the other $2$ of every $3$ must be green.

2. If there are $24$ marbles in the bag, how many are green?

If the probability of picking a green marble is two-thirds, that means two-thirds of the marbles are green. What is two-thirds of $24$?

How could you represent two-thirds in a fraction with the denominator, or bottom number, of $24$? The numerator, or number on top, will be the number of green marbles.