[Korokian]

I need help on how to find out the composition( mass % Cu and mass % Zn) of pre- and post- 1982 pennies.
Using the values below, how can i determine the composition of Cu and Zn in pre- and post- 1982 pennies?

density of copper= 8.96g/mL
density of zinc= 7.14g/mL
Density of pre-1982 pennies= 8.1g/mL
Density of post-1982 pennies= 7.9g/mL

[enahs]

Pre-1982
(8.96g/ml * x ) + (7.14g/ml * y) = 8.1

Where x and y are the percent. I.E. 88% is 0.88. So 100 * 0.88 gives you 88, which is 88 percent.

When you have just two percents of one thing, they both must add up to 1 , so you can replace y with (1-x)

So now you have
(8.96g/ml * x) + (7.14g/ml * 1-x ) = 8.1
Solve for x (algebra and quadratic). You then get the percent composition for x (which how I have the numbers arranged, Copper). Zinc percent composition is then just 1-x.
In this case so you can know you are getting the math correct, I will tell you that by those numbers pre-82 Cu was 0.5274 (* 100) = 52.74 %, and so Zn is 47.26%.

Repeat for post-1982. This is just basic algebra practice.

[Korokian]

thanks man you reassured me