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

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

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

834 would be rounded** down **to **800. **

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

If the digit in the tenths column (to the right of the decimal point) is **less than 5**, the number needs to be **rounded down**.

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

3.9 wouold be rounded to **4**

**What is 8.42 rounded to one decimal place?**

If the digit to the right of the tenths (the hundredths column) is **less than 5,** the number needs to be **rounded down.**

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

8.42 has a 2 in the hundredths column, so it rounds down to **8.4**

**Example:**

Estimate the answer to the addition by first rounding the decimal number.

10 + 1.42 rounded to one decimal place.

10 is already rounded.

1.42 rounds down to 1.4

**10 + 1.42 =** **10 + 1.4 = 11.4**

Let's have a go at some questions now.