Rounding

You do not always need to know the exact number. You can use numbers that are approximate by estimating or rounding off.

When you are rounding a number to the nearest 10, you are trying to find out which multiple of 10 the number is closest to. The rule is that if a number is exactly halfway between two multiples of 10, you always round up.

Look at the ones digit:

• If it is less than 5 then round the number down by changing the ones digit to zero.

• If it is 5 or more than round the number up by adding one to the tens digit and changing the ones digit to zero.

1. • • 38 rounds up to 40 because the ones digit is 8.

     • 64 rounds down to 60 because the ones digit is 4.

     • 135 rounds up to 140 because the ones digit is a 5.

Remember: It is important to know the place value chart when rounding off numbers.

For example: Let’s round 12,837 to the nearest thousand.

1. Underline the number in the place you are rounding off to. 12, 837

1. Look at the number in the next place to the right. 12,[8]37

2. Eight is greater than 5, so add 1 to the underlined number.

3. Now, change all the numbers to the right of the underlined number to 0.

4. The rounded off number is 13,000 because 12,800 is closer to 13,000 than to 12,000.

Let’s try another. Round $538.00 to the nearest hundred dollars. Follow the above steps.

1. $538.00

2. $5[3]8.00

3. Three is less than 5, so leave the bold number as it is and don’t forget to change all the numbers on the right to 0.

4. The rounded off number is $500.00.

Here’s a tricky one to try.

Let’s round 3,983,542 to the nearest hundred thousand.

1. 3,983,542

2. 3,9[8]3,542 - [find the hundred thousand place]

3. Eight is greater than 5, so we round UP: add 1 to 9. But when we change the 9 to 10, we can only put the 0 in the hundred thousands place, so we must add the 1 to the 3 to make 4.

4. The rounded off number is 4,000,000.

Now its your turn...