word problem

Question

Each marble bag sold by Rachel's Marble Company contains
4
red marbles for every
5
yellow marbles. If a bag has
45
yellow marbles, how many red marbles does it contain?

Answer 1

We have a proportional relationship, or ratio, being expressed in this problem. The ratio of red to yellow marbles is 4:5 or 4/5. If the bag has 45 yellow marbles, we need to determine how many red marbles are in the bag. Since the number of red marbles is the unknown quantity, we can represent this as x. Hence, we have the following equation:

 

4/5 = x/45

 

5x = 180

 

x = 36

 

The number of red marbles is 36

 

If we write the fraction 36/45, we see that the numerator and denominator share a common factor of 9. Therefore, 36/45 reduces to 4/5, which is our original ratio. 

Answer 2

Use a proportion (red:yellow) and you will have an easy equation to solve for the unknown.