Numbers can grow into the thousands and beyond. Once you know the value of each digit, even big numbers are easy to read.
Why this matters: Rounding helps us estimate quickly. If a football stadium holds 42,800 people, we can just say "about 43,000" so everyone understands.
Place value
Each digit sits in a column. The column tells you what the digit is worth.
| Ten thousands | Thousands | Hundreds | Tens | Ones |
|---|---|---|---|---|
| 3 | 6 | 4 | 2 | 5 |
So 36,425 means 3 ten thousands, 6 thousands, 4 hundreds, 2 tens and 5 ones.
Rounding
Rounding means changing a number to the nearest tidy number. Look at the digit just to the right of the place you are rounding to.
- If it is 5 or more, round up.
- If it is 4 or less, round down (stay the same).
Round 4,270 to the nearest 100. Look at the tens digit: 7. That is 5 or more, so round up to 4,300.
Round 8,240 to the nearest 1,000. Look at the hundreds digit: 2. That is 4 or less, so round down to 8,000.
Estimating
To estimate an answer, round each number first, then add. To guess 3,900 + 6,100, round to 4,000 + 6,000 = about 10,000.
Put these numbers in order, smallest first:
- 4,270
- 8,240
- 36,425
Try it: which ten is nearest?
Tap 47. Is it nearer to 40 or to 50?