When adding and subtracting larger numbers it can be useful to be able to check to see if our answers are reasonable.

**Rounding **the numbers we are adding/subtracting is a useful way of doing this.

In this activity, we will be looking at how to round numbers to the **nearest 100** in order to check that answers to addition and subtraction questions are reasonable.

Rules for rounding to the nearest 100:

When rounding to the nearest 100, we look at the **tens digit.**

If the tens digit is** less than 5,** the number is rounded **down.**

If the tens digit is** 5 or more**, the number is rounded **up.**

Any digit in the ones column becomes a zero.

Let's look at some examples of rounding to the nearest 100.

**Remember, we look at the tens column.**

** **

744 would be rounded down to 700 because there is a 4 in the tens column.

751 would be rounded up to 800 because there is a 5 in the tens column.

8,264 would be rounded up to 8,300 because there is a 6 in the tens column (even though this is a 4-digit number, we are still rounding to the nearest 100)

Now let's use rounding to check if the answer to a subtraction is reasonable:

1,232 - 673 = 559

Now, let's round the numbers:

**1,232 rounds down to 1,200 (there is a 3 in the tens column)**

**673 rounds up to 700 (there is a 7 in the tens column)**

1,200 - 700 = 500

So, 559 is a reasonable answer to the original question.

Now, it's your turn to have a go at some questions!

Don't forget - some will be addition and others subtraction!