Mixture...5

A tank has a capacity of 10 gallons. When it is full, it contains 15% alcohol. How many gallons must be replaced by an 80% alcohol solution to give 10 gallons of 70% solution?

Let g = number of gallons that must be replaced.

Original - removed + added = results

10(0.15) - (10 - g) + 0.80g = 10(0.70)

Yes?

 

Your "10- g" is wrong. It is the number of gallons of liquid left in the tank after g gallons are removed NOT the amount of alcohol removed. The amount of alcohol removed is 0.15g.
10(0.15)- 0.15g+ 0.80g= 10(0.70)
1.5+ 0.65g= 7

 

You see how easy it is just to reply.