Estimation Strategies and Rounding Rules

When rounding, you will need to know which place value you will need to round to. When you find out which place to round to you can determine whether or not to round up or down based on the number to the right of the target place value. If the number is from 0-4, round down. If the number to the right of the target place value is 5-9, round up. For example, to round 123.234 to the nearest hundredth, you must look to the thousandth place to determine whether or not to round up or down. Because the thousandths place is 4, you will round down, giving you an answer of 123.23.

Estimation Strategies and Rounding Rules

Hey guys! Welcome to this video on Rounding and Estimation.

Rounding and estimation are helpful tools that allow us to simplify numbers so that they are easier for our brains to work with.

When rounding, the first thing you need to decide is your “round-off” digit. For instance, let’s say you are asked to round a number to the nearest hundreds place. The round-off digit is the digit in the hundreds place. The round-off digit is always the place value of the number that you are rounding to.

Once you know your round-off number, you then need to look at the very next number to the right of that round-off digit. If that number is less than 5, then the round-off digit stays the same and you change everything to the right to 0s. If that number is 5 or greater, add 1 to the round off digit and change everything to the right of it to 0s..

Let’s look at an example:

Round 7,890.45 to the nearest hundred place.

So, we need to find our round-off digit, which is the number in the hundreds place, so 8. Now, look at the digit one place to the right, which is 9. 9 is more than 5, so our round-off digit 8 needs to be rounded up. So, we add one to the round-off digit, and change everything to the right to 0s. So that gives us 7,900.00. But since everything to the right is already 0s, we don’t really need this decimal place so we can just rewrite this as 7,900.

Let’s look at another example.

Round 37.9824 to the nearest thousandth.

Remember thousandth is not the same as thousand. Thousandth lets us know that we are dealing with a decimal number, and thousand lets us know we are dealing with a whole number.

So, let’s find our round-off digit, which is 2. Now, look at the number to the right of that round-off digit, which is 4. Since 4 is less than 5, the round-off digit stays the same, and everything to the right of it can be dropped.

So, our answer then would be 37.982, and we drop the last digit.

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Frequently Asked Questions

Q

How do you round to the nearest hundred?

A

Round a number to the nearest hundred by determining if the number in the tens place is greater than or equal to 5. If the tens place is greater than or equal to 5, increase the hundreds place by 1. If the tens place is less than 5, keep the hundreds place the same. Then, change every number after the hundreds place to a 0.
Ex. Round 6, 852 to the nearest hundred.
Look at the tens place. Since 5 ≥ 5, increase the hundreds place by 1 and replace every number after with a 0. 6,852 rounded to the nearest hundred is 6,900.

Q

How do you round to the nearest tenth?

A

Round to the nearest tenth by looking at the hundredth place. If it is greater than or equal to 5, round the tenth place up one digit. If it is less than 5, keep the tenths place the same. Don’t write any numbers after the tenths place.
Ex. Round 16.423 to the nearest tenth.
Find the hundredths place: 2. 2 is less than 5, so round down (tenths place stays the same). Only write up to the tenths place. 16.423 rounds to 16.4

Q

How do you round decimals?

A

Round decimals the same way you round non-decimal numbers. Check the number in the place value one below the one you are rounding to. If it is greater than or equal to 5, round up. If it is less than 5, round down. Then, only write the numbers until you reach the place you are rounding to.
Ex. Round 8.715 to the nearest whole number.
Since 7 is greater than 5, round up. 8.715 rounds to 9.
Ex. Round 63.271 to the nearest hundredth.
Since 1 is less than 5, round down. 63.271 rounds to 63.27.

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by Mometrix Test Preparation | Last Updated: January 5, 2021