a.u.s nickel contains 3.9g of copper and 1.2g of nickel.

copper/nickel=3.9/1.2=3.25

500*3.25=1625 kg of copper

You also can write fraction:

3.9/1.2=x/500

1.2*x=3.9*500

1.2*x=1950 Divide with 1.2

x=1950/1.2

x=1625

1,625

1625

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1625

Correct!