math
posted by jay on .
A scientist wants to combine two metal alloys into 20 kg of a third alloy which is 60% aluminum. He plans to use one alloy with 45% aluminum content, and a second alloy with 70% aluminum content. How many kilograms of each alloy must be combined?

Number of kg of 45% alum .... x
number of kg of 70% alum .... 20x
solve for x
.45x + .70(20x) = .60(20)
(I suggest multiplying each of the 3 term by 100 first)