Keli is celebrating her birthday and she wants a ratio of red balloons to blue balloons that is 4:3. If she ordered 21 balloons for her party how many would she have of each color?

12 red and 9 blue.

4+3=7

21/7=3

3x4=12 red

3x3=9 blue

Let's call the # of blue balloons = B and the # of green balloons = G

We know that B + G = 21 balloons in total, and that the ratio of B:G = 4:3

From there, we can see that if B/G = 4/3, 3B = 4G

Now, let's substitute one for the other - since B + G = 21 → B = 21 - G

3 * (21 - G) = 4G → 63 - 3G = 4G → 63 = 7G → 9 = G

Since B + G = 21 and G = 9, there were 12 blue balloons at Kali's party.