0580

Number Toolkit

Number

Column addition

  • Write the numbers one above the other with the place-value columns lined up
  • Add each column working right to left
  • When a column totals ten or more, write the ones digit below the line and carry the tens digit into the next column

Column subtraction

  • Write the number being subtracted underneath the number it is taken from
  • Work right to left, and where the upper digit is too small, exchange one unit down from the neighbouring column
  • Exchanging turns one unit of the left-hand column into ten of the current column
Worked example

Column addition with carrying

Work out 4 726 + 895 without a calculator.

Solution:

  • Estimate first: 4 700 + 900 = 5 600
  • Ones: 6 + 5 = 11, so write 1 and carry 1
  • Tens: 2 + 9 + 1 = 12, so write 2 and carry 1
  • Hundreds: 7 + 8 + 1 = 16, so write 6 and carry 1
  • Thousands: 4 + 1 = 5
  • The total is 5 621, which is close to the estimate of 5 600