Au. s nickel contains 3.9 g of copper and 1.2 g of nickel. how many kilograms of copper must be combined with 500 kg of nickel to make nickel coins?

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.

Copper/nickel=3.9/1.2=3.25 

500*3.25=1625 kg of copper