And has some dimes and quarters. If she has 20 coins worth a total of $3.80, how many of each type of coin does she have?

D + q = 20 ... d = 20 - q

0.10d + 0.25q = 3.80

0.10 (20 - q) + 0.25q = 3.80

2 - 0.10q + 0.25q = 3.80

-0.10q + 0.25q = 3.80 - 2

0.15q = 1.80

q = 1.80/0.15

q = 12 < = = = 12 quarters

d + q = 20

d + 12 = 20

d = 20 - 12

d = 8 < = = 8 dimes

12 quarters and 8 dimes. Ask me if you have any questions