Subtraction Term Two 2012

Over the last few weeks we have been exploring strategies to help us solve problems involving subtraction.  We have discovered some generalisations about subtraction and some strategies that help us work out facts more quickly:

  • Subtracting 0 from a number gets the same number.
  • Subtracting 1 from a number gets the number that is one less.
  • Subtracting the same number gets 0. 4-4=0; 6-6=0; etc.
  • “Think Addition” – what number can you add to the number you are subtracting to get the starting number. For example, 9-4=__. What number can you add to 4 to get 9.
  • When subtracting 9, think subtract 10 and then add one on
  • Count backwards. We have a number line in the back of the room or students can make their own on their paper. For the problem 13-5=___, start on 13 and count back 5.

We have also used a number chart to help count back bigger numbers.  Some students have explored using an empty number line and this week we are going to try using a strategy called partitioning.

What strategy do you like to help solve subtraction equations?

Here are some websites that can help you practice getting quicker at recalling subtraction facts:

http://oswego.org/ocsd-web/games/mathmagician/mathssub.html

http://www.arcademicskillbuilders.com/games/sailboat-subtraction/sailboat-subtraction.html