Matt has 20 coins in his back pack, all dimes and quarters. The value of a dime is $0.10 and the value of a quarter is $0.25. If the value of the coins is $3.95, how many of each coin does he have?

Question

And I have to find the variables, equation and solution

Answer 1

D+Q = 20 is the 1st equation

.10D +.25Q = 3.95 is the 2nd equation

.10D+.10Q = 2.00

subtract .10 times 1st equation from the 2nd equation to get

.15Q = 1.95

Q = 1.95/.15 = 13 Quarters

D= 20-13= 7 Dimes

check the answers, plug them into the 2nd equation

.1(7) +.25(13) = .70+3.25 = 3.95