Finding the number of red disks

Mike has 72 solid-colored disks that are either red, blue, or green. Once lined up, he finds that there are 15 more red disks than green and 9 more green disks than blue. How many red disks does he have?

I know the answer is 37 but I don't see how to set it up.

Re: Finding the number of red disks

Quote:

Originally Posted by

**dannyc** Mike has 72 solid-colored disks that are either red, blue, or green. Once lined up, he finds that there are 15 more red disks than green and 9 more green disks than blue. How many red disks does he have?

I know the answer is 37 but I don't see how to set it up.

number of red = x

number of green = x-15

number of blue = x-15-9 = x-24

Then x+x+x-15-24 = 72

Re: Finding the number of red disks

Quote:

Originally Posted by

**dannyc** Mike has 72 solid-colored disks that are either red, blue, or green. Once lined up, he finds that there are 15 more red disks than green and 9 more green disks than blue. How many red disks does he have? I know the answer is 37 but I don't see how to set it up.

$\displaystyle \begin{align*}r &=g+15\\ g &= b+9\\ r+g+b &=72 \end{align*}$