Answer: 12 pounds of coffe worth $10 a pound should be added
Step-by-step explanation:
Let x represent the number of pounds of coffee worth $10 a pound that should be added. The total cost of x pounds would be $10x
It was added to 30 pounds of coffee worth $3 a pound. Total cost of this coffee = 3 × 30 = 90
The mixture made is worth $5 per pound. The total cost of the mixture would be
5(x + 30) = 5x + 150
Therefore,
10x + 90 = 5x + 150
10x - 5x = 150 - 90
5x = 60
x = 60/5 = 12