Question

Please Help!

An alloy is a mixture of metals. Suppose that a certain alloy is made by mixing 5 grams of an alloy containing 12% copper with 78 grams of an alloy containing 92%copper.
Do not do any rounding.
(a) How many grams of copper are in the resulting mixture?
grams

(b) What percentage of the resulting mixture is copper?
%

Answer 1

(a)
Copper content
=5g*12% + 78g*92%
=0.60+71.76 g
=72,.36 g

(b)
percentage of copper in resulting mixture
=72.36/(5+78)
=1809/2075
=7236/83%   (=87.18% approximately, but instructions say do not round)

Answer 2

1) Let A₁ be the 1st alloyed mixed with A₂, the 2nd alloyed.
Amount of cooper in
A₁ = 5x12% = 0.6 g of cooper
A₂ = 78x92% = 71.76 g of cooper
Total Amount of cooper in A₁+A₂ = 72.36 g of cooper

2) Total amount used for the mixture/ total amount of cooper:
 72.36/(5+78) = 72.36/83 = 0.8718 = 87.18% of cooper