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Addition within a hundred

You learn to add and subtract to 100 by keeping the tens and the ones apart.

Practise thisWhiteboardMake it a quiz

How to work it out

  1. Split both numbers into tens and ones.
  2. Calculate the tens with tens.
  3. Calculate the ones with ones.
  4. Add the two results together.
JumpingJump along the number line
SplittingTens and ones apart

A worked example

65 + 22

  1. Tens: 60 + 20 = 80.
  2. Ones: 5 + 2 = 7.
  3. Put them together: 80 + 7 = 87.
More examples

76 − 12

  1. Tens: 70 − 10 = 60.
  2. Ones: 6 − 2 = 4.
  3. Put them together: 60 + 4 = 64.
JumpingJump along the number line
SplittingTens and ones apart

44 + 25

  1. Tens: 40 + 20 = 60.
  2. Ones: 4 + 5 = 9.
  3. Put them together: 60 + 9 = 69.
JumpingJump along the number line
SplittingTens and ones apart

Try it yourself

  1. Draw jumps on the number line

    23 + 6 =

  2. 44 + 25 =

Practise this

Watch out

  • You mix up the digits: for 56 + 20 you add the 2 to the 6 and get 58.

    Look carefully at which digit is the tens. The 2 in 20 goes with the 50, not with the 6.

  • When you subtract, you swap the ones round: for 73 − 15 you do 5 − 3.

    Always take the second number away from the first. If that does not work, go back to the ten first.

Tips

  • Say out loud which digits are tens and which are ones.

Exceptions

  • If the ones cross ten, like 48 + 27, you need to bridge through ten.

Why it works

65 is 6 tens and 5 ones. Keep tens with tens and ones with ones, and you only work with small sums you already know. That works for adding and for subtracting.