Functional Skills: Rounding and Estimating

Skill 1: Rounding to a Number of Decimal Places

Example: Round 17.268 to 2 decimal places.

Step 1: Find the digit you are rounding to. In this case it is the 2nd digit after the decimal point.

17.2\textcolor{red}{6} 8

Step 2: If the number to the right is below 5, we round down and it stays the same. If it is 5 or more, we round up and increase it by 1.

8 is bigger than 5, so the 6 increases by 1 to 7

Step 3: Don’t write down and digits after this. What it remaining is the final answer, which is

17.2\textcolor{red}{7}

Skill 2: Rounding to the Nearest Whole Number

Example: Round 53.182 to the nearest whole number.

Step 1: Find the digit you are rounding to. In this case it is the first digit before the decimal point, since we are rounding to the nearest whole number.

5\textcolor{orange}{3}.182

Step 2: If the number to the right is below 5, we round down and it stays the same. If it is 5 or more, we round up and increase it by 1.

1 is smaller than 5, so the 3 stays the same.

Step 3: Don’t write down any digits after this, including the decimal point. What it remaining is the final answer, which is

5\textcolor{orange}{3}

Skill 3: Rounding to the Nearest 10

Example: Round 365 to the nearest ten.

Step 1: The first digit, 3, is in the hundreds column, but the second digit, 6, is in the tens column, so this is the digit we are rounding to.

3\textcolor{orange}{6}5

Step 2: If the number to the right is below 5, we round down and it stays the same. If it is 5 or more, we round up and increase it by 1.

5 is 5 or more, so the 6 is increased by 1 to 7.

Step 3: Finally, change all of the digits after this to \textcolor{limegreen}{0}‘s. What it remaining is the final answer, which is

3\textcolor{orange}{7}\textcolor{limegreen}{0}

Skill 4: Rounding to the Nearest 100

Example: Round 4179 to the nearest hundred.

Step 1: The first digit, 4, is in the thousands column, but the second digit, 1, is in the hundreds column, so this is the digit we are rounding to.

4\textcolor{orange}{1}79

Step 2: If the number to the right is below 5, we round down and it stays the same. If it is 5 or more, we round up and increase it by 1.

7 is 5 or more, so the 1 is increased by 1 to 2.

Step 3: Finally, change all of the digits after this to \textcolor{limegreen}{0}‘s. What it remaining is the final answer, which is

4\textcolor{orange}{2}\textcolor{limegreen}{00}

Note: We use similar techniques to round to the nearest 1000, 10000, etc.

Skill 5: Estimating

Answers to calculations can be estimated by rounding the numbers in them to the nearest whole number, or nearest 10, etc. This can be used to check your calculations are correct or estimate the answer without a calculator.

Example: Stevie sells some items on an auction website.

She sells a TV for £178.50, a microwave for £32.85 and a hairdryer for £27.10

Estimate how much money Stevie makes from selling these items.

 

Since the value of the items are all in the tens or hundreds, it would be better to round them all to the nearest 10.

£178.50 rounds to \textcolor{purple}{£180}

£32.85 rounds to \textcolor{purple}{£30}

£27.10 rounds to \textcolor{purple}{£30}

So, in total she makes

\textcolor{purple}{£180} + \textcolor{purple}{£30}+ \textcolor{purple}{£30} = \textcolor{purple}{£240}