Addition with two-digit numbers - KS1 Maths - Year 1

Place value in two-digit numbers

When you are solving an addition calculation with a two-digit number, you need to think about tens and ones.

A place value chart can help you to see the value of each digit in a number.

For example, here is the number 23 represented in a place value chart with counters.

You can see that the number 23 is made of 2 tens and 3 ones.

Complete this interactive to learn more about adding with two-digit numbers and then put your knowledge to the test with this quiz.

To add two-digit numbers, you need to think about place value.

You start by adding up how many ones you have. If you have more than 10 ones, you can put a group of ten into the tens column.

You then add up how many tens you have.

By adding the tens and the ones together, you can find out how many you have altogether.

Let’s use these pencils and a place value chart to help us find the answer to 17 + 8.

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The number 17 is made of 1 group of ten and 7 ones. You can show this by putting a pack of 10 pencils in the tens column and 7 individual pencils in the ones column. Then the calculation is asking you to add 8 more pencils.
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Start by adding up how many ones you have. So let's add the pencils in the ones column. If you know your number bonds to 10, then you know that 7 + 8 is going to be more than 10...
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7 + 8 = 15. By adding the pencils in the ones column you can make a new group of ten. This can then be moved across into the tens column of the place value chart.
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You can then add up how many tens and ones you have. You can see there are 2 groups of ten and 5 ones. So the answer to 17 + 8 is 25.