A word for every ten
Every tens number has a word of its own: twenty, thirty, forty, fifty, sixty, seventy, eighty and ninety. Twenty is 2 tens, thirty is 3 tens, and so on up to ninety, which is 9 tens.
Most of these words sound like the number of tens they count: six and sixty, seven and seventy. Forty is the one to watch when you write it. It is spelled forty, with no u, even though four has one.
Tens first, then ones
A number such as 47 is made of 4 tens and 7 ones. Its word says the tens first and then the ones: 4 tens is forty, 7 ones is seven, so 47 is forty-seven.
The small line between forty and seven is a hyphen. It joins the two words into the name of one number. The word follows the digits from left to right: the 4 on the left gives forty, and the 7 on the right gives seven.
4 tens and 7 ones: forty-seven.
Reading a number the right way round
Swapping the two parts makes a different number. Seventy-four is 7 tens and 4 ones, which is 74, not 47. So when you hear a number word, write the tens digit for the first part and the ones digit for the second part.
Reading the digits one at a time is the other slip. 47 is not "four-seven": the 4 stands for 4 tens, which is forty.
The teens
The numbers from 11 to 19 have 1 ten and some ones. Eleven and twelve have names of their own. From thirteen to nineteen, the words say the ones first: thirteen is three and ten, fifteen is five and ten, and eighteen is eight and ten.
Because the ones are said first, it is easy to write them first. Fifteen is not 51. It has 1 ten and 5 ones, so it is written 15, with the 1 on the left, just like every other number.
Fifteen is 1 ten and 5 ones. The word says five first, but the number is still written 15.
Past a hundred
A 3-digit number says its biggest place first, then the rest in the way you already know. 345 is 3 hundreds, 4 tens and 5 ones. Say the hundreds, three hundred, and then the tens and ones, forty-five. So 345 is three hundred forty-five.
Many people say "three hundred and forty-five". The word and changes nothing: both say the same number.
3 hundreds, 4 tens and 5 ones: three hundred forty-five.
A place with nothing in it
Four hundred six has 4 hundreds and 6 ones, and the words say nothing about tens. There are 0 tens, so write 0 in the tens place: 406. The 0 keeps the 4 in the hundreds place.
Without the 0 the number becomes 46, which is forty-six. And writing 4006 puts too many places in: four hundred six is 400 + 6, a number with only three digits.
4 hundreds, no tens and 6 ones: 406, four hundred six.
Worked example: A Number in Words with an Empty Place
Question Tom's ticket says four hundred and six. Ben's ticket says 640. (a) Write the number on Tom's ticket in digits. (b) Write the number on Ben's ticket in words.
1.Draw a chart with three places: hundreds, tens and ones. Four hundred goes in the hundreds place as 4. Six goes in the ones place as 6.
Four hundred is 4 in the hundreds place. Six is 6 in the ones place. 2.The words say nothing about tens, so there are 0 tens. Write 0 in the tens place. The 0 keeps the 4 in the hundreds place.
The words say nothing about tens, so the tens place gets a 0. 3.(a) The number on Tom's ticket is 406.
(a) The number on Tom's ticket is 406. 4.Now put 640 in the chart: 6 hundreds, 4 tens and 0 ones. Say the hundreds first and then the tens.
640 is 6 hundreds, 4 tens and 0 ones. Say the hundreds first and then the tens. 5.(b) 6 hundreds is six hundred and 4 tens is forty. There are no ones to say. The number on Ben's ticket is six hundred and forty.
(b) 6 hundreds is six hundred and 4 tens is forty. The number is six hundred and forty.
Answer: (a) 406; (b) six hundred and forty
Common mistakes
- Writing 46 for four hundred and six. Without the 0, the 4 moves into the tens place and the number becomes forty-six.
- Writing 4006. Four hundred and six is 400 + 6, which has only three places. It is not 400 with a 6 written after it.