Mathnasium 51 E. Main Street, Avon CT 06001 (860) 785-6284

Contact Us for More Information

* indicates a required field
  • phone number format invalid
  • email format invalid
Problems detected, please review the form.
protected by reCAPTCHA
Privacy - Terms

News from Mathnasium of Avon

Dollars and Decimals

Jul 5, 2019

One important reason for kids to learn decimals is that the decimal system is what we use for money. 

If you have three quarters, do you have enough to pay for an 89-cent lemonade?

If you give a cashier three dollars to pay for an ice cream treat that costs $2.25, how much change will you get? 

Can you come up with a combination of eight coins that adds up to one dollar?

On July 6, 1785, the U.S. Congress adopted the dollar as the unit of currency and the decimal system for money. This would greatly simplify monetary calculations. Before that, money in the American colonies was a mishmash of different denominations and values based on British, Spanish and other coins. There was a $30 bill as well as bills of 3 dollars, 6 dollars, 4 dollars, and 8 dollars, and some worth 1/6, 1/3 and 2/3 of a dollar. Not only that, but each colony had its own system.

Thomas Jefferson was in favor of using a decimal system for money; he imagined the difficulties of a schoolchild using the British system at the time: 

“puzzled with adding the farthings, taking out the fours and carrying them on; adding the pence, taking out the twelves and carrying them on; adding the shillings, taking out the twenties and carrying them on." 

"But when he came to the pounds," Jefferson continued, "where he had only tens to carry forward, it was easy and free from error." 

"Even mathematical heads," he admitted, "feel the relief of an easier substituted for a more difficult process." 1


Once the decimal system was adopted, everything could be calculated in tenths and hundredths of a dollar. A penny is one hundredth of a dollar, a nickel is five hundredths of a dollar, a dime ten hundredths (or one tenth) of a dollar, and a quarter is 25 hundredths (which happens to equal one fourth) of a dollar. 

Having a decimal system for money means that we don’t have to add fractions when we’re working with money. Adding fractions is still an important skill, but it can require more steps than simple decimal addition. So if you think adding up all those coins is tough, just be glad it’s not farthings and two-thirds-dollar notes!




U.S. National Archives and Records Administration:

National Museum of American History: