I cant figure out how to work this problem out and how they came up with the answer of 60lbs. A merchant has coffee worth $40 a pound that she wishes to mix with 20 pounds of coffee worth $80 a pound to get a mixture that can be sold for $50 a pound. How many pounds of the $40 coffee should be used?
Let amount of $40-per lb coffee to mix, be F
Then total cost of the $40-per lb coffee = 40F
Total cost of the $80-per lb coffee: 20(80), or $1,600
Total cost of entire mixture: 40F + 1,600, and total weight is: F + 20
We then get:
50(F + 20) = 40F + 1.600 ------ Cross-multiplying
50F + 1,000 = 40F + 1,600
50F - 40F = 1,600 - 1,000
10F = 600
F, or amount of $40-per lb coffee to mix = , or lbs