This table shows the number of marbles in a bag by color. If one marble is randomly selected from the bag, what is the probability that it will be a blue or a red marble?

I would say it would be in the middle

Step-by-step explanation:

the answer would be 52% :)

Step-by-step explanation:

We have 10 ml of 20% acid to which we need to add "x" milliliters of 100% acid to make 50% acid.
 
.20 * 10 + 1.00x = .50 * (10 +x)
in which "x" is the volume of the 100% acid to be added.
2 + x = 5 + .5 x
.5x = 3
x = 6 milliliters

Source:
http://www.1728.org/mixture.htm
Scroll down to problem B