Question 99077
Let x=amount of 10% mixture that he used
(1)  Now the amount of pure isopropyl in this mixture is 0.10x

(2)  Amount of pure isopropyl in the 20% mixture is 0.20(60)

(3)  Amount of pure isopropyl in the final mixture is 0.16(60+x)

Now we know that 1+2=3. So our equation to solve is:

0.10x+0.20*60=0.16(60+x)  get rid of parens

0.10x+12=9.6+0.16x subtract 9.6 and also 0.10x from both sides

0.10x-0.10x+12-9.6=9.6-9.6+0.16x-0.10x  collect like terms

2.4=0.06x  divide both sides by 0.06

x=40 gal--------------------amount of 10% solution used

CK

0.10*40+0.20*60=0.16*100
4+12=16

16=16

Hope this helps---ptaylor