Please explain example.

Question

Two artists are mixing up green paint for a mural. The first artist, Shane, mixes 3 parts blue and 2 parts yellow to make a shade of green. The second artist, Nora, mixes 5 parts blue and 3 parts yellow to make another shade of green. After Nora mixes her paint, she has 72 ounces of green paint. How many ounces of yellow and blue paint did she use in her mixture? 

Answer 1

A mixture of 5 parts blue and 3 parts yellow has a total of 8 parts. The green paint is made of all the parts so we can write the following ratios to find the number of ounces for each color (blue and yellow):

5 blue = x

8 total 72 ounces

Multiply by the numerator and denominator by 9:

5 blue = 45 ounces blue

8 total 72 ounces

For yellow:

3 yellow = x

8 total 72 ounces

Multiply by the numerator and denominator by 9:

3 yellow = 27 ounces yellow

8 total 72 ounces

You could also subtract 45 from 72:

72 - 45 = 27 ounces yellow