Math CentralQuandaries & Queries


Question from Patti:

A copy machine accepts nickels, dimes, and quarters. After 1 hour, there are 30 coins total, and their value is $\$5.10.$ How many nickels, quarters, and dimes are in the machine? (Hint: There are exactly five different solutions.)

Hi Patti:

I can show you one approach.

You could make the $\$5.10$ entirely in nickels but that would be 110 coins, far too many. Maybe it's better to start by maximizing the number of quarters rather than nickels.

You can make $\$5.00$ with 20 quarters and then the remaining $\$0.10$ with one dime or two nickels but in either case it is too few coins. To increase the number of coins trade in one quarter for 2 dimes and 1 nickel. Thus you have made $\$5.00$ with 22 coins. If you convert the 2 dimes to 4 nickels and make the remaining $\$0.10$ out of nickels but that is still too few coins.

Next I would try 18 quarters.

I hope this helps,

About Math Central
* Registered trade mark of Imperial Oil Limited. Used under license.


Math Central is supported by the University of Regina and the Imperial Oil Foundation.
Quandaries & Queries page Home page University of Regina Imperial Oil Foundation