Large numbers and other numerals · Usually met around P5
Rounding and estimating large numbers
Look one place to the right: 0–4 down, 5–9 up.
How to do it
Method
Look one place to the right: 0–4 down, 5–9 up
18,653,000 ≈ 18,650,000 (thousands digit 3: down)
Another way
Number line
Between 18,650,000 and 18,660,000: nearer the first
In full
To round to a place, look only at the digit just to its right: 0 to 4, every digit after the place becomes 0 (round down); 5 to 9, add 1 to the place (round up). 18,653,000 to the nearest ten thousand: the thousands digit is 3, so round down to 18,650,000. Or think of a number line: 18,653,000 lies between 18,650,000 and 18,660,000 and is closer to 18,650,000. Big numbers are often written in thousands, millions or billions: 15,000 = 15 thousand, 2,300,000 = 2.3 million, 4,500,000,000 = 4.5 billion. To estimate a huge quantity, count a small part and multiply by how many such parts there are: about 40 people a square, 200 squares, about 8000 people.
Worked examples
Have a go first, then open each one for the answer and the working.
Example 1
Round 81,623,151 to the nearest ten thousand. About how many times 10,000 is it?
Show the answer and working
Answer: 8162 × 10,000
Look at the thousands digit, 3: 0–4 rounds down, 5–9 adds 1 to the ten thousands. So it is about 8162 × 10,000.
Example 2
Round 2,806,746,900 to the nearest hundred million. About how many times 100,000,000 is it?
Show the answer and working
Answer: 28 × 100,000,000
Look at the ten millions digit, 0: 0–4 down, 5–9 up. About 28 × 100,000,000.
Example 3
Round 27,373,582 to the nearest hundred thousand. Which is the result?
- A. 27,400,000
- B. 27,000,000
- C. 27,370,000
- D. 27,300,000
Choose the right answer
Show the answer and working
Answer: A. 27,400,000
Look at the ten thousands digit: 7 ≥ 5, so add 1 to the hundred thousands and zero the rest: 27,400,000.
Practise it in the game →Large numbers and other numerals · Free to start, unlimited questions, no download