Answer:
15 nickels
25 dimes
Explanation:
Letting
x = nickels
y = dimes
We create a system of equations
x + y = 40
0.05x + 0.10y = 3.15
Let's take the first one and subtract the X
y = 40 - x
Now we can substitute that into the second equation
0.05x + 0.10(40-x) = 3.15
0.05x + 4 - .10x = 3.15
0.05x = 0.75
Those last steps were just combining like terms. Now we divide by 0.05
x = 15 nickels
Now we can use the original equation and plug in 15 for x
15 + y = 40
y = 25 dimes