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Adding three numbers, step by step

A column with three numbers in it is not just a longer sum.

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The question

95 + 61 + 21

1 95 61 21 177
  1. 95 + 61 + 21, written in columns. Start at the RIGHT, with the ones — and watch the carry: with several numbers it can be a 2, not just a 1.
  2. 5 + 1 + 1 makes 7. Write 7 in the ones.
  3. 9 + 6 + 2 makes 17. Too big for one column, so write 7 in the tens and carry 1 to the left.
  4. Nothing left to add in the hundreds, but 1 was carried in — so the hundreds is 1.
  5. That is the whole sum: 95 + 61 + 21 = 177. Check it by adding each column upwards instead of downwards — a different order, so a slip is unlikely to repeat itself.

How it works.

  1. 01

    95 + 61 + 21, written in columns. Start at the RIGHT, with the ones — and watch the carry: with several numbers it can be a 2, not just a 1.

  2. 02

    5 + 1 + 1 makes 7. Write 7 in the ones.

  3. 03

    9 + 6 + 2 makes 17. Too big for one column, so write 7 in the tens and carry 1 to the left.

  4. 04

    Nothing left to add in the hundreds, but 1 was carried in — so the hundreds is 1.

  5. 05

    That is the whole sum: 95 + 61 + 21 = 177. Check it by adding each column upwards instead of downwards — a different order, so a slip is unlikely to repeat itself.

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