Expert: Lynn Houston - 5/12/2010

Question
Have 2 blue blocks in bag. how many red blocks need to be added to bag to get a red block 2/3of the time??

Answer
4 red blocks will give you a 4/6 (or 2/3) shot of getting a red block. The way I figured that is:

r = red blocks
b = blue blocks = 2

r/(r+b) = 2/3
r/(r+2) = 2/3  multiply both sides of equation by 3(r+2)
3r = 2(r+2)
3r = 2r + 4   subtract 2r from both sides
r = 4