Question

18 carat gold is an alloy containing gold and another metal in the ratio by mass:

3 : 1

If an 18 carat gold ingot has a mass of 250 g, what mass of gold was used to make the alloy?

Answer 1

we know that
the ratio is 3 : 1 by mass
that means
(3+1)=4 g
for every 4 grams of 18 carat gold there are 3 grams of gold
so
4/3=250/x----> 4*x=3*250-----> x=3*250/4----> x=187.5 g

the answer is
187.5 g