college algebra
posted by college .
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 420kilogram mixture.
my calculations all came out super wrong

If there are x kg of Brazilian coffee, then the rest (420x) is Turkish. So,
10x + 13(420x) = 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.