Thursday, September 15, 2011
36 Club Subtraction tips
This only works when the top number in the tens column is less than the bottom number in the tens column like this.
A lot of kids freak at this because they don't have eighteen fingers. So I tell them to subtract upside down. Take 8 from 9 and get 1. If the upside down answer is 1 then the answer to the problem is 9.
If the upside down answer is 2, then the answer is 8. (3 - 7 and 4 - 6.)
Go back to 18 - 9. If 18 were one more (19) then the answer to the problem would be 10. But 18 is one less than 19 so the answer is one less than 10. Notice the pairs always add up to ten.
This works because if the top number is 2 away from giving you the answer of 10, then the answer is 2 from 10 or 8.
If your child doesn't understand the upside down terminology, try the 1 from ten or 2 from ten. They can use this method for more complicated math, just don't let them forget that they still have to borrow!
I'd love to know if this helps anyone.
Addition Facts Here