Question 473272
a 10% acid solution is to be mixed with a 50% solution to get 200 litres of a 20% solution. how many litres of each solution should be used?
let x = 10%
let y = 50% 
x + y = 200
   y= 200 -x
0.10x+0.50y = 200* 0.20
 substitution : y= 200 -x
0.10x+0.50(200-x) = 200* 0.20
0.10x + 100- 0.50x = 40
             -0.4x = 40 -100
                 x= -60/-0.4
                 x=15
substitution : x = 15 find y
15 + y = 200
     y = 200-15
      y = 185

10% acid solution is should be used 15 litres
50% acid solution is should be used 185 litres