Add and subtract 2-digit and 1-digit numbers

Learning focus

Learn about adding and subtracting a 2-digit number and a 1-digit number (for example 12 + 7 = 19 or 45 + 3 = 48).

This lesson includes:

  • one learning summary
  • two activities

Learn

Adding a one-digit number and a two-digit number

To add a one-digit number to a two-digit number, start with the bigger number and count forwards with the smaller number.

43 (larger number) + 8 (smaller number) = 51

You could find the number on a number square and count forwards. Find number 43, then count forwards 8 ones to get 51.

Subtracting a one-digit number from a two-digit number

To subtract a one-digit number from a two-digit number, you also start with the bigger number, but you count backwards.

Try it on the 100 square above.

43 - 8 = 35

Adding two two-digit numbers

When a number problem uses two two-digit numbers, we break down the numbers into tens and ones.

55 + 34 = ?

Start with the tens and add them together.

5 tens + 3 tens = 8 tens

or

50+ 30 = 80

Then add the ones.

5 ones + 4 ones = 9 ones

or 5 + 4 = 9

Finally add both answers together.

80 + 9 = 89

Subtracting a two-digit number from a two-digit number

To subtract a two-digit number from a two-digit number we count back the tens of the smaller number and then count back the ones.

58 – 44 = ?

44 has 4 tens so we count back 4 tens from the bigger number 58.

58 count back 4 tens: 58, 48, 38, 28, 18

Finally use this answer and then count back the ones:

18 – 4 = 14

58 – 44 = 14

Top Tip

You can use a one hundred square to help you count backwards and forwards.

Practise

Activity 1

Adding quiz

Get a piece of paper and a pencil, then listen to this quiz. You only have 10 seconds to answer each question so write the answers down quickly!

Finished? Check your answers here. The questions are also written out, if you can't listen to the quiz out loud.

Activity 2

Have a go at the quiz below.

Play

Play Guardians: Defenders of Mathematica to learn more about this topic and test your skills.

Guardians: Defenders of Mathematica

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