Metalworker has a metal alloy that is 25% copper and another alloy that is 70% copper. How many kilograms of each alloy should the metalworker combine to create 50kg of a 52% copper alloy

x = amount (kg) of 25% coper alloy

y = amount (also kg) of 70% copper alloy

Each kilogram of the 25% alloy contains 0.25 kg of copper, while each kilogram of the 70% alloy contains 0.7 kg of copper. When combined, the metalworker ends up with (x + y) kg of an alloy that should consist of 52% copper, so that it contains 0.52 (x + y) kg of copper.

The metalworker wants to make 50 kg of this new alloy, so that

x + y = 50

of which 52%, 0.52 (50 kg) = 26 kg, is copper, so

0.25x + 0.7y = 26

Solve for y in terms of x :

y = 50 - x

Substitute this into the other equation and solve for x :

0.25x + 0.7 (50 - x) = 26

0.25x + 35 - 0.7x = 26

9 = 0.45x

x = 20   →  y = 30

example 2 – simplify: step 1: completely factor both the numerators and denominators of all fractions. step 2: change the division sign to a multiplication sign and flip (or reciprocate) the fraction after the division sign; essential you need to multiply by the reciprocal. step 3 : cancel or reduce the fractions.