Question 597082
A certain metal is 40% tin.
 How many kilograms of this metal must be mixed with 80 kilograms of a metal that is 70% tin to get a metal that is 50% tin?
:
let x = amt of 40% tin

:
A typical mixture equation
.40x + .70(80) = .50(x+80)
.40x + 56 = .50x + 40
56 - 40 = .50x - .40x
16 = .10x
x = 16/.1
x = 160 km of 40% tin required