Question 607388
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Hi
Let x= amount of 40%, y= amount of 80% 
0.40x + 0.80y = 0.5(20)
 x + y = 20 OR x = 20-y
good Work! substituting (20-y) for x
0.40(20-y) + 0.80y = 0.5(20)
  .40y = .5(20)-.40(20)
     y = .10(20)/.40
     y = 5 gal of the 80% solution and 15gal of the 40% solution (5 + 15 = 20)