Respuesta :
Answer: he needs to combine 18 kg
of the 20% copper alloy and 72 kg of the 75% copper alloy.
Step-by-step explanation:
Let x represent the number of kilograms of the 20% copper alloy that he needs to use.
Let y represent the number of kilograms of the 75% copper alloy that he needs to use.
The mass of the copper to be created is 90 kg. It means that
x + y = 90
The amount copper in the first alloy is 20/100 × x = 0.2x
The amount copper in the second alloy is 75/100 × y = 0.75y
The amount of copper in the alloy to be created is
64/100 × 90 = 57.6
The equation would be
0.2x + 0.75y = 57.6- - - - - -- - - - - 1
Substituting x = 90 - y into equation 1, it becomes
0.2(90 - y) + 0.75y = 57.6
18 - 0.2y + 0.75y = 57.6
- 0.2y + 0.75y = 57.6 - 18
0.55y = 39.6
y = 39.6/0.55
y = 72
x = 90 - y = 90 - 72
x = 18
