Question

in a certain chemical, the ratio of zinc to copper is 4 of 13. a jar of the chemical contains 338 grams of copper. how many grams of zinc does it contain?

Answer 1

4:13 is the ratio for zinc to copper.  That means for every 4 grams of zinc you have to have 13 grams of copper.

They tell you that you have 338 grams of copper.

4     X
---   ---
13   338

Cross multiple would be 4(338) = 13x
Simplify
1352 = 13x
104=x

104 grams of zinc

Answer 2

If the ratio of zinc to copper is 4 TO 13, then do this.

4/13 = x/338

13x = 338 * 4

13x = 1352

x = 104

It contains 104 grams of zinc.