Arithmetic Grade Four

Lesson Twenty-eight: Rounding to Nearest 10

You probably know how to count by tens. Starting with ten and counting by tens we can count by ten like this: 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 210, 220, etc.

When we round to the nearest ten we say that the number we are given is closest to one of these multiples of ten. For instance, the number 74 rounded to the nearest 10 is 70. If we look at a number line 74 is part way between 70 and 80. It happens to be closer to 70 and so when we round 74 off to the nearest 10 it becomes 70.

Here are a few examples: 


  66 -> 70		122 -> 120		139 -> 140

 219 -> 220		 61 -> 60		988 -> 990

 543 -> 540		 17 -> 20		999 -> 1000
Rules for rounding:
  1. If the number in the ones column is 4 or less round down. Example: 42 -> 40.
  2. If the number in the ones column is 5 or more round up. Example: 45 -> 50.
Special Case:

If you have a number like 495 you have to remember that it will have to round up to 500. Many times students are confused by this situation.

Continue to next page of lesson