We can estimate answers to complicated additions by rounding both decimals to the nearest whole number before adding them together.

**How to round decimals to whole numbers **

Look at the number directly to the right of the decimal point, that is the number in the **tenths** position.

If that number is less than 5, we round down so that we simply remove the numbers after the decimal point.

**For example**: 32.46 rounds down to 32 because the number in the tenths place is a 4.

159.08 rounds down to 159 because there is a zero in the tenths place.

If the number in the tenths place is 5 or more, we round up.

**For example**: 72.6 rounds up to 73 because the number in the tenths place is a 6.

197.57 rounds up to 198 because the number in the tenths place is a 5.

Having seen how to round decimals to the nearest whole number, let's look at how to use this to estimate addition of decimals.

**Example:**

64.51 + 18.15 can be estimated by rounding both decimals to the nearest whole number first: 64.51 rounds up to 65 and 18.15 rounds down to 18.

65 + 18 = 83

So the answer is 83.

Let's have a go at some questions now.