In this activity, we will be rounding decimal numbers to the nearest whole number and then estimating the answer to an addition.

**Recap of rounding**

**What is 35 rounded to the** **nearest 10**?

If the number in the ones column is **less than 5**, the number needs to be **rounded down**.

If the number in the ones column is** 5 or above**, the number needs to be **rounded up**.

So 35 would be rounded **up** to **40.**

**What is 834 rounded to the nearest 100?**

If the number in the tens column is** less than 5**, the number needs to be **rounded down**.

If the number in the tens column is** 5 or above**, the number needs to be **rounded up.**

834 would be rounded **down** to **800 **because the tens digit is less than 5.

**What is 3.9 rounded to the nearest whole number?**

If the number in the tenths column (the first one after the decimal point) is **less than 5**, the number **rounds down.**

If the number in the tenths column is **5 or above**, the number **rounds up**.

3.9 has a 9 in the tenths column, so it rounds **up** to** 4.**

**Example**

Estimate the answer to the addition by first rounding the decimal numbers to the nearest whole number.

10.2 + 1.4

10.2 has a 2 in the tenths column, and 1.4 has a 4 in the tenths column, so they both **round down**:

**10.2 + 1.4 =** **10 + 1 = 11**

Now it's your turn!