Subtraction Methods

On Wednesday we looked at new methods to subtract. We used the Cuisenaire rods instead of Numicon to help us make the numbers.

The purple rod is worth 10, the white cube is worth 1. The green rod is worth 6. We found that the yellow rod filled the gap (it is worth 5).

20 – 6. We used the cubes worth 1 to find the difference. We found that there were 14 cubes. 14 is the answer.

This method is good because it is easier to solve problems with bigger numbers and it helps us with our expanded written methods, something that some of us moved on to.

Expanded Subtraction

To use the expanded method we partition the numbers involved and record them above each other.

34 – 21 =

(30 + 4)        This is like making the top number with the rods.
(20 + 1) –       This is like the bottom number using the rods
10 + 3 = 13      We subtract the top number from the bottom to quickly find the answer.