3. The materials to make 25kg of an alloy of copper and zinc cost $124. If the copper costs $6.40/kg and the zinc cost $2.80/kg, find the composition of alloy.

The composition is;

10 kg of copper and 15 kg of zinc

Step-by-step explanation:

let the weight of zinc be z and that of copper be c

The addition of both will give 25 kg

thus;

z + c = 25 ••••••(i)

secondly;

6.40(c) + 2.80(z) = 124

6.40c + 2.80z = 124 ••••••(ii)

from the first equation;

z = 25-c

substitute this into the second equation;

6.4c + 2.8(25-c) = 124

6.4c + 70 - 2.8c = 124

6.4c-2.8c = 124-70

3.6c = 54

c = 54/3.6

c = 15

Recall;

z = 25-c

z = 25-15

c = 10

1 is c

2 is a

3 is a

step-by-step explanation: