x = # dimes
y = # quarters
x+y = 20 so x = 20 - y
0.1x + 0.25y = 4.1
substitute x = 20 - y into 0.1x + 0.25y = 4.1
0.1x + 0.25y = 4.1
0.1(20 - y) + 0.25y = 4.1
2 - 0.1y + 0.25y = 4.1
0.15y = 2.1
y = 2.1 / 0.15
y = 14
x = 20 - 14 = 6
answer
Dimes: 6 coins
Quarters: 14 coins
Double check
6 + 14 = 20 coins total
6(0.1) + 14(0.25) = 0.6 + 3.5 = $4.10
