Question

An alloy is a mixture of metals. Suppose that a certain alloy is made by mixing 90grams of an alloy containing 15% copper with 70 grams of an alloy containing 35% copper. Answer the questions below. Do not do any rounding. (a) How many grams of copper are in the resulting mixture?

(a)       _____ grams

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

Answer 1

(a) The 1st alloy weighs 90 gms of which 15% is copper. Therefore weight of copper = (15/100) * 90 = 13.5gms

The 2nd alloy weighs 70 gms of which 35% is copper. Therefore weight of copper = (35/100) * 70 = 24.5gms

Therefore the total weight of copper in the resulting misture = 24.5 + 13.5 = 38 grams.

(b) The weight of the total mixture is 90 + 70 = 160 grams, of which 38 grams is copper.

Therefore % of copper in the resulting mixture = (38/160) * 100 = 23.75%.