Holly,

Thank you for your message. I did mention your question to Dr. Cotter and her advice was as follows....


In the check number world, 9s are zeroes. This happens in some other worlds also. With clocks 2 hours after 11:00 p.m. isn't 13:00 p.m.; it's 1:00. (This type of arithmetic is called modular arithmetic.)

For checking subtraction with check numbers, it's easier to add up. For example,

36 (0)
- 8 (8)
28 (1)

Instead of doing (0) - (8), add (1) + (8) = (0). So it checks.

I hope this helps, please let me know if you have any further questions. We would be happy to help.

Make it a great day,

Cassie
Activities for Learning-RightStart™ Mathematics
Cassie@ALabacus.com
www.ALabacus.com

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