A two-digit number is built from tens and ones. In 35 the left digit counts tens and the right digit counts ones, so 35 is 3 tens (30) and 5 ones. When you hear 'thirty-five', the 'thirty' already fills the tens column, so the 5 sits in the ones column beside it — you do not write 30 and 5 next to each other. Say the tens digit first and write it on the left, then the ones digit on the right.
Explore this idea with maths tools
Build a number
2 tens + 4 ones = 20 + 4 = 24
Move from 29 to 30. Ten ones become one ten. The amount stays the same when you regroup.
Words to know
- digit
- a single number symbol from 0 to 9
- place value
- the value a digit has because of its column
- ones
- the right-hand column, worth one each
Worked examples
thirty-five
- 1.3 tens and 5 ones.
- 2.30 + 5 = 35.
= 35
forty-two
- 1.4 tens and 2 ones.
- 2.40 + 2 = 42.
= 42
sixty
- 1.6 tens and 0 ones.
- 2.60 + 0 = 60.
= 60
For parents
Method: Base-ten blocks: ten-rods for tens, unit-cubes for ones.
What to say: Ask 'how many tens? how many ones?' then write the tens digit on the left.
Common mistakes:
- Writing 'thirty-five' as 305 (both parts in full).
- Reversing the digits to 53.
- Adding the digits: 3 tens and 5 ones read as 8.