Category: Arithmetic

  • How to Multiply By Hand Without Hurting Your Brain

    How to Multiply By Hand Without Hurting Your Brain

    There’s an amazingly fancy tool that I began discussing in the last post. This D-word probably has been a close friend of yours for a while. It’s likely you’ve used it before and just didn’t realize it.

    Well, now you can give it a name and give it some practice. It’s the Distributive Property.

    Fancy name. Fabulous friend.

    Check out what’s really going on with  87 x 48 here…

    That one you can do quickly with pencil and paper. Here’s an easier one that you are more likely to do in your head (after practice with P&P of course)…

    Have you done this before? Share your stories in the comments.

  • How to Subtract Using Reverse Addition

    How to Subtract Using Reverse Addition

    This was requested by Jake’s Mom. Since she was taught to borrow, she was dumfounded at what Jake brought home. Happily, Jake is young enough and unscathed enough to not balk at a “different” method than what his mom was taught. He got it right away.

    But Jake’s mom, on the other hand, is struggling.

    If your kiddo is being taught this, here’s a way to look at it that might help you understand what’s going on.

    First, a brief review on the relationship of subtraction to addition:

    Here’s what “reverse addition” looks like in relation to our old friend “borrowing,” using the same example:

    And here’s an example:

    Another example (along with a special tip for you):

    And a final example, just to help you get the hang of it.

    Still have questions? Post them in the comments.

    Thanks, Jake’s Mom, for the question!