Answer: 7 pounds of peanuts and 3 pounds of cashew should be used.
Explanation:
Let x represent the number of pounds of peanuts that he would use in the mixture.
Let y represent the number of pounds of cashews that he would use in the mixture.
The total mixture would be 10 pounds. It means that
x + y = 10
The mixture of peanuts and cashews would be sold at $4.75 per pound. This means that the total cost of the mixture is
10 × 4.75 = $47.5
If peanuts cost $4.00 per pound and cashews cost $6.50 per pound, it means that
4x + 6.5y = 47.5- - - - - - - - - - - - 1
Substituting x = 10 - y into equation 1, it becomes
4(10 - y) + 6.5y = 47.5
40 - 4y + 6.5y = 47.5
- 4y + 6.5y = 47.5 - 40
2.5y = 7.5
y = 7.5/2.5
y = 3
x = 10 - y = 10 - 3
x = 7