Jose's dimes and nickels total $6.10. If the dimes were replaced by pennies then he would have $3.49. How many of each coin does he have?
Call the number of dimes = D = number of pennies and the number of nickels = N
So....we have these equations
Value of a dime * number of dimes + Value of a nickel * number of nickles = 6.10
.10D + .05N = 6.10 (1)
And
Value of penny * number + Value of a nickel * number = 3.49
.01 (D ) + .05N = 3.49 (2)
Subtract (2) from (1)
.09 D = 2.61
D = 2.61 / .09 = 29 = number of dimes = number of pennies
And to find the number of nickels, use ( 1)
.10 (29) + .05N = 6.10
2.90 +.05N = 6.10
.05N = 6.10 - 2.90
.05N = 3.20
N = 3.20 / .05 = 64 = number of nickels