SAT Word Problem Solve?

Question

an artist makes a certain shade of green paint by mixing blue and yellow in a ratio of 3:4 . She makes orange by mixing red and yellow in a ratio of 2:3. If on one day she mixes both green and orange and uses equal amount of blue and red paint, what fraction part of the paint is yellow.

Answer 1

Where in the world did you get a 31 from? When you add up the four parts (b+2yellows+r), shouldn't you get 29 as the total amount?

It should be 17/29

Answer 2

Well, you need the least common multiple for red and blue, which would be 6. Multiply the ratio involving blue by 2 and the one involving red by 3. now you have:
6:8 - blue:yellow
6:9 - red:yellow
So she uses 8 parts blue paint, 6 parts red paint, and 17 parts yellow paint (8 + 9). So to get the fractional part of yellow paint she uses, divide the total amount of paint by the amount of yellow paint.
17 / (8 + 6 + 17)
17 / (31)
17/31 of the paint is yellow paint.