Before measuring something, you need to know what unit to use. You can do this by estimating its approximate size. For measures such as speed you will use a formula.

Part of

To check the accuracy of a rounded number, you need to find the largest and smallest numbers that it could have been rounded from.

- Question
Q1. The number of children in a school is , correct to the nearest . What is the largest possible and smallest possible number of children in the school?

Q2. Amelia spends in the local supermarket, correct to the nearest . What is the greatest and least amount that Amelia could have spent?

**A1.**The number of children in the school has been rounded to the nearest to give .

The answer is and .

The smallest number that rounds to is .

The largest number that rounds to is .

So, the smallest possible number of children in the school is , and the largest possible number of children is .

Note: is exactly halfway between and , but rounds up to give , so we use .

**A2.**The answer is and .

The smallest number that rounds to is .

The largest number that rounds to is .

Remember that is halfway between and , but rounds up to , so we must go for the smallest possible unit less than (in this case a penny less), which is .