learnbits.app· Geography

Addition with tens and ones

You learn to add tens and ones: first the tens, then the ones.

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How to work it out

  1. Split the second number into tens and ones.
  2. Add the tens first.
  3. Then add the ones.

A worked example

56 + 28

  1. Partition 28 into 20 and 8.
  2. Add the tens: 56 + 20 = 76.
  3. Add the ones: 76 + 8 = 84.
More examples

45 + 27

  1. Partition 27 into 20 and 7.
  2. Add the tens: 45 + 20 = 65.
  3. Add the ones: 65 + 7 = 72.

36 + 47

  1. Partition 47 into 40 and 7.
  2. Add the tens: 36 + 40 = 76.
  3. Add the ones: 76 + 7 = 83.

Try it yourself

  1. 55 + 36 =

  2. 45 + 27 =

Watch out

  • You forget the extra ten: for 56 + 28 you say 74.

    For 76 + 8 you go past 80. Bridge through the ten: 76 + 4 = 80 and 80 + 4 = 84.

Tips

  • Partition the second number into tens and ones, and you have two easy sums.
  • Start with the bigger number and add the smaller one to it.

Exceptions

  • If the ones add up to more than 10, like 48 + 27, jump to the ten in the second step.

Why it works

For 56 + 28 there is a lot to do at once. If you partition 28 into 20 and 8, you do two small sums one after the other. Do the tens first, because they change the number the most.