Here's solving another type of subtraction sum.
Let's work on this sum.
First lay 4 ten stamps and 5 one stamps accordingly on the mat.
We need to take 8 ones away.
Looking at the One column on the green mat, we can see that we have insufficient one stamps to subtract from.
This is where we 'borrow' 1 ten stamp from the tens column and shift it over to the ones column.
1 ten stamp is equivalent to 10 one stamps (this is a pre requisite knowledge the child must posses before doing this activity). Exchange the blue stamp for 10 green stamps & remove the blue stamp away from the mat.
Now you have a total of 15 one stamps.
On paper, it should now look like this.
Point out to the child that now only 3 ten stamps are left on the mat.
So now, we have enough one stamps to remove 8 green stamps.
We are required to substract 2 tens away, remove 2 blue stamps accordingly.
Finally, you get your answer.