Arithmetic Grade Four

Lesson Twenty-nine: Rounding to Nearest 100

Counting by 100's is even easier than counting by tens! Starting with one 100 and counting by hundreds we can count by one hundred like this: 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1100, 1200, 1300, 1400, 1500, 1600, 1700, 1800, 1900, 2000, 2100, 2200, etc.

When we round to the nearest hundred we say that the number we are given is closest to one of these multiples of one hundred. For instance, the number 374 rounded to the nearest 100 is 400. If we look at a number line 374 is part way between 300 and 400. It happens to be closer to 400 and so when we round 374 off to the nearest 100 it becomes 400.

Here are a few examples: 


  366 -> 400		1226 -> 1200		1399 -> 1400

 2139 -> 2100		 6123 -> 6100		9881 -> 9900

 5435 -> 5400		 173 -> 200		9299 -> 9300
Rounding to the Nearest 100

Consider the following examples: 


     1222 -> 1200              1388 -> 1400              1111 -> 1100
      899 ->  900               566 ->  600            23,555 -> 23,600
     1988 -> 2000              2391 -> 2400             2349  -> 2300
     3450 -> 3500              9999 -> 10000            2150  -> 2200
Rules for rounding to nearest 100:
  1. If the number in the tens column is 4 or less, then round down. (Example: 544 -> 500.)
  2. If the number in the tens column is 5 or more, then round up. (Example: 550 -> 600.)
Special Case:

If you get a number like 2950, it rounds up to 3000. Many students are confused by these kinds of problems.

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