What you need to know
Every place in a number is worth ten times the place to its right: ones, tens, hundreds, thousands, ten thousands, hundred thousands, millions. In Australia we write large numbers with a small space between each group of three digits, which makes them easier to read: 3 456 782 is read as three million, four hundred and fifty-six thousand, seven hundred and eighty-two.
| Millions | Hundred thousands | Ten thousands | Thousands | Hundreds | Tens | Ones |
|---|
| 3 | 4 | 5 | 6 | 7 | 8 | 2 |
| 1 | 0 | 5 | 0 | 3 | 0 | 9 |
The second row of the table is 1 050 309 (one million, fifty thousand, three hundred and nine). The zeros are placeholders: they hold the hundred thousands, thousands and tens places so that the other digits stay in the right columns. The value of a digit depends on its place, so in 3 456 782 the 5 is worth 50 000 and the 4 is worth 400 000.
Write 2 070 415 in words and in expanded form
- Read the groups of three from the left: 2 | 070 | 415.
- Words: two million, seventy thousand, four hundred and fifteen.
- Expanded form adds the value of each non-zero digit: 2 000 000 + 70 000 + 400 + 10 + 5.
- Check by adding: 2 000 000 + 70 000 = 2 070 000, and 2 070 000 + 415 = 2 070 415.
Which is larger: 1 345 902 or 1 354 092?
- Both numbers have 7 digits, so compare from the left, place by place.
- Millions: 1 and 1, the same. Hundred thousands: 3 and 3, the same.
- Ten thousands: 4 and 5. Since 5 is bigger, 1 354 092 is larger. You can stop as soon as you find a difference.
Rounding. Find the digit in the place you are rounding to, then look only at the digit immediately to its right. If that digit is 5 or more, round up (add 1 to the rounding digit). If it is 4 or less, leave the rounding digit alone. Then change every digit to the right of the rounding place to zero.
Round 3 456 782 to the nearest thousand, ten thousand and million
- Nearest thousand: the thousands digit is 6, and the digit to its right is 7. Round up: 3 457 000.
- Nearest ten thousand: the ten thousands digit is 5, and the digit to its right is 6. Round up: 3 460 000.
- Nearest million: the millions digit is 3, and the digit to its right is 4. Stay the same: 3 000 000.
Round 849 500 to the nearest hundred thousand
- The hundred thousands digit is 8.
- The digit to its right (ten thousands) is 4, which is less than 5.
- So the 8 stays and everything after it becomes zero: 800 000.
- It is not 900 000, even though 49 500 feels close to 50 000. Only the next digit decides.
Common mistake: leaving out placeholder zeros. Two million and six thousand is 2 006 000, not 26 000. Set out a place value chart, fill in the digits you know, and put a zero in every empty place.
Common mistake: looking at all the digits to the right when rounding instead of just the next one. 849 500 rounds to 800 000 to the nearest hundred thousand because the ten thousands digit is 4.
Check yourself
- Write 5 208 316 in words.
- What is the value of the 7 in 4 718 250?
- Write in digits: six million, forty thousand and nine.
- Which is larger: 2 987 654 or 3 001 000?
- Round 6 384 912 to the nearest ten thousand.
- Round 7 650 000 to the nearest million.
Answers: 1. five million, two hundred and eight thousand, three hundred and sixteen 2. 700 000 3. 6 040 009 4. 3 001 000 5. 6 380 000 (the ten thousands digit is 8 and the next digit is 4) 6. 8 000 000 (the millions digit is 7 and the next digit is 6, so round up)