There are 9 coins in a piggy bank in terms of dimes and nickels and the value of the dimes is 15 cents more than the value of the nickels. Find out how many of each coin there is.
d = 9 - n
10d - 5n = 15
Substitute 9-n for d in second equation and solve for n. Insert that value into the first equation and solve for d. Check by inserting both values into the second equation.