Write and solve an equation of ratios to solve this problem:
3.9 g copper 1.2 g nickel
----------------- = ----------------
x 500 kg
Then, cross multiplying, we get
(3.9 g copper)(500 kg) = (1.2 g nickel)*x
Divide both sides by (1.2 g nickel) to learn the # of kg of copper needed.
