Teaching Students About Rounding Numbers: Tips and Strategies

Ideas for Teaching How to Round Numbers

Why Round Numbers?

When you round a number, you replace it with a different number that has approximately the same value, but is a simpler, shorter or more specific portrayal of the number. For example, you might replace:

• 15/77 with 1/5
• $2.679 wth $2.68
• 3.141592653… with 3.14

When you round a number, you do it to have a number that is easier to write or to work with. Occasionally you do it to express the correctness of a calculated or estimated number. For example, consider a number that was calculated as 2,468, but has been established to be accurate within several hundred units. In this case, it might better use 'about 2,500.'

In addition to rounding to a particular unit, students are sometimes asked to 'round to the greatest place.' This means to round a number based on the number next to it. Here are some examples:

• 16 becomes 20, but 14 becomes 10
• 378 becomes 400, but 339 becomes 300
• 1432 becomes 1000, but 1532 becomes 2000

Ways to Teach Round Numbers

A common teaching practice is to begin with something visual or with a manipulative. Then, have the students demonstrate the same concept in a similar fashion. A range of possible activities may then be used to aid in retention of the material - in this case, rounding.

Hands-On or Visual Activities

A variety of hands-on activities may be used to demonstrate rounding. An ongoing discussion - as opposed to a lecture - will enhance these activities.

1. Fill up glasses or water bottles with varying amounts of water. Ask students to determine if the water level is closer to the top or the bottom of the glass.
   
   
2. Use a picture of a steep hill, with the number five at the sharply rounded top of the hill and the numbers 0-4 going up the hill on the left and 6-10 going down the hill on the right. Have a picture of a car that can go up and down the hill and stop at any of the numbers. On the way up, if they stop, the car will roll down the hill to the next lower number.
   
   On the way down, if they stop, the car will roll down that side of the hill to the next higher number. If they teetering at the top, they will soon start to roll down the right side of the hill because the motor end of the car weighs more than the end with an empty trunk.
   
   
3. Use a number line. Show that a given number, such as 24, is closer to 20 than 30. Repeat the process with other numbers, like 156, which is closer to 160 than 150.

Active Games

This game begins with a story. Make up your own story of an animal, such as a squirrel, that is going to cross the street. He gets just a little ways across when a big truck comes rumbling along. Because the squirrel is only a little way from the curb where he started, he quickly runs back. Each time he tries to cross, he gets a little further than the time before, always going to the curb that is closest. When he is in the exact middle of the street, it is easier to keep going across than to turn around and go back.

The game is played outside. Parallel lines representing 'curbs' are drawn, and lines for the numbers 1-9 (or 10-90, 100-900 - whichever kind of rounding you're working on) are drawn between them. Students (squirrels) start at one 'curb.' When you say, 'Start,' they begin to dash across the 'street.' When you say, 'Truck,' they must stop, decide which curb to go to and tell you why. As they get better at it, they can immediately go to that curb and then tell you what number they reached before the 'truck came along' and why they proceeded to the curb they went to.

Songs and Cadences

There are a number of songs that teach rounding rules, such as Slip to the Side by Joe Crone on his Geometry Park CD. Teachers sometimes make up their own military-style cadences or songs to familiar tunes such as If You're Happy and You Know It, Clap Your Hands. You can also check out YouTube.com to find other rounding numbers songs or a rounding rap.