Sheila mixed 3 ounces of blue paint with 2 ounces of yellow paint. she decied to create 20 ounces of the same mixture. how many ounces of yellow paint does sheila need for the mixture ?

Sheila mixed 3 ounces of blue paint and 2 ounces of yellow paint.
So the total of the two mixtures is:
3 + 2 = 5 So 5 ounces have been produced by Sheila already.
So the mixture requires 2/5 yellow paint.
The total mixture of yellow an blue paint will be 20 ounces.
So
Amount of yellow paint required = (2/5) * 20
                                                   = 8
So 8 ounces of yellow paint is required by Sheila for making a 20 ounces of paint mixture.