store mixes a Brazilian coffee worth worth $10 per kilogram and a turkish coffee worth $13 per kilogram. The mixture is to sell for $12 per kilogram. Find out how much of each should be used to make a 420-kilogram mixture.

Question

my calculations all came out super wrong

Answer 1

If there are x kg of Brazilian coffee, then the rest (420-x) is Turkish. So,

10x + 13(420-x) = 12*420
x = 140

Note that 140 is 1/3 of 420, meaning that it drags the price down 1/3 of the way from 13 to 10, or $12.