Question

How much of an alloy 30% copper must be added to 25 pounds of a second alloy which is 20% copper to create a 27% alloy?

Answer 1

30%=.3 20%=.2 27%=.27

our unknown is the weight if the 30% and the total weight if the resulting alloy is 25+our unknown

we will call our unknown x, so

`x * .3 + 25 * .2 = (x + 25) * .27`
solve for x


`.3x + 5.0 = .27x + 6.75 \\ .3x - .27x + 5.0 = .27x - .27x + 6.75 \\ .03x + 5.0 = 6.75 \\ .03x + 5.0 - 5.0 = 6.75 - 5.0 \\ .03x = 1.75 \\ (.03x)/(.03) = (1.75)/(.03) \\ x = 58.33`