In order to make estimations, your child will need to be able to round numbers. The same rules apply for rounding a whole number, decimal or fraction. To round a number, you first need to decide what place value you’d like to round to. Next, you look at the number to the right of the place value you’ve chosen. If the number to the right is 5 or greater (5,6,7,8, or 9), you will round up. This means you will make the number in the place value you’ve chosen one more. For example, if we were rounding 638 to the nearest 10, 3 is in the tens place. The number to the right of the 3 is 8. The number 8 is equal to or greater than 5, so you will round up. This means the number in the tens place, 3 will be made one more, 4. So, 638 rounded to the nearest ten is 640. Notice how the 8 has been replaced with a zero. The last step of any rounding problem is replacing all numbers to the right of the place value you’re looking at with zeros. Now, if the number to the right of the place value you have chosen is 4 or less (4, 3, 2, 1, 0), you will round down. This means you will keep the number in the place value you have chosen and replace all numbers to the right with 0s to make the number less (rounded down). For example, if we were rounding 4,358 to the nearest thousand, 4 is in the thousands place. To the right of the 4 is a 3. Three is 4 or less, so we will round down. To do this we will keep the 4 and replace every number behind it with a 0. So, 4,358 is 4,000 when rounded down. One mistake commonly made by children in rounding down a number is that they make the number in the place value they are looking at one less. Watch or this and show your child how making this mistake ruins an estimate, because the rounded number is much less than the original number. If, for instance, this mistake were made for the problem above, we would get 3,000 instead of 4,000. As we can see, 3,000 is nowhere near 4,358.
An alternative to teaching rounding is to have your child write down both choices for rounding and then choosing the one that is less for rounded down and more for rounded up. An example of how to do this is shown below.
Round the number 12,082 to the nearest hundred.
Choices: rounded down 12,000 or rounded up 12,100
Look at the number to the right of the hundreds place (8). Round up.
This strategy works well for visual and kinesthetic learners. Have kinesthetic learners touch and read aloud each place value starting with one. Have them stop with their finger on the hundreds place. Next, have him/her write down the choices, touching and saying each one. Lastly, have your child point to the number to the write of the hundreds place. Ask if that number is greater or less than 5. Since it is greater, have your child put his/her finger on the greater estimate.