1 half dollar = 50 cents

1 quarter = 25 cents

1 dime = 10 cents

let

h = the number of half-dollars

q = the number of quarters

d = the number of dimes

she has the same amount of quarters as half dollars

q = h

My sister has $24.25 = 2425 cents in her piggy bank made up of quarters, dimes, and half-dollars

50h + 25q + 10d = 2425 divide both sides by 5

10h + 5q + 2d = 485

since q = h we can write

10h + 5h + 2d = 485

2d = 485 - 15h

2d = 5(97 - 3h)

d = (1/2)(97 - 3h) is the number of dimes.