Numbers to 1000
Estimating and rounding
You do not always need to know exactly how many there are. Often an estimate is enough. You can estimate by giving a range, or by rounding to the nearest 10 or 100.
Estimating with a range
An estimate is a sensible guess. Instead of one number you can give a range, like 'about 200 to 300 beans'. A range shows the number is somewhere between two values.
Rounding to the nearest 10
To round to the nearest 10, look at the ones digit. • If it is 5 or more, round up. • If it is less than 5, round down. Example: 72 rounds to 70 (2 is less than 5). 29 rounds to 30 (9 is 5 or more). 45 rounds up to 50.
Rounding to the nearest 100
To round to the nearest 100, look at the tens digit. • If it is 5 or more, round up. • If it is less than 5, round down. Example: 123 rounds to 100 (2 tens is less than 5). 678 rounds to 700 (7 tens is 5 or more). 471 rounds to 500.
Worked examples
Rounding to the nearest 10
- Round 72. Look at the ones digit, which is 2.
- 2 is less than 5, so round down.
Answer: 72 rounds to 70.
Rounding to the nearest 100
- Round 678. Look at the tens digit, which is 7.
- 7 is 5 or more, so round up.
Answer: 678 rounds to 700.
Estimating with the bean table
- Every 10 grams of beans is about 100 beans.
- Arun's beans weigh 78 grams, which is between 70 and 80 grams.
Answer: A good estimate is about 700 to 800 beans.
Where you see this in real life
- Guessing about how many sweets are in a jar.
- Estimating how many people are at a party.
- Rounding a price to the nearest 10 dollars.
Key words
- Estimate
- A sensible guess when you do not need the exact number.
- Range
- Two numbers that a value lies between, like 200 to 300.
- Round
- To change a number to a nearby tidy number, like the nearest 10 or 100.
- Round up
- To make a number the next 10 or 100 up.
- Round down
- To make a number the 10 or 100 below it.