Answer
You will need 4.4 lbs of the cheaper chocolate and 6 lbs of the expensive chocolate.
Explanation
Let the amount to be made of the type of chocolate (cheaper chocolate) that sells for $5.00/lb be x pounds.
Let the amount to be made of the type of chocolate (expensive chocolate) that sells for $7.60/lb be y pounds.
We would like to make a chocolate mixture that weighs 10.4 lbs. That is,
x + y = 10.4 .......... equation 1
This chocolate mixture is supposed to cost $6.50/lb and weigh 10.4 lbs. Hence, the cost of 10.4 lbs of this chocolate mixture will be
= 6.50 × 10.4 = $67.6
The cost of x pounds of the $5.00/lb = x × 5 = 5x dollars
The cost of y pounds of the $7.60/lb = y × 7.60 = 7.6y dollars
The cost of the two types of chocolate have to amount to $67.6
5x + 7.6y = 67.6 .......... equation 2
Writing the two equations together
x + y = 10.4
5x + 7.6y = 67.6
This simultaneous equation is then solved and the solution obtained is
x = 4.4 pounds and y = 6 pounds.
Hope this Helps!!!