Input data
2 type of coins
Customer 1
8 coins, 3 of which are nickles
Customer 2
11 coins, 7 of which are nickles
Procedure
V = total value
Customer 1
V = (8-3)c + (3)*0.05
Customer 2
V = (11-7)c + (7)*0.05
Now we are going to equal the equations
The coin c would be c = 0.20