you need to explain why this works. yours is not to reason why, just invert and multiply won't get it these days
You are not explaining to the students why this works. This isn't Common Core learning is it?
Do you teach your students why the "flip and multiply" rule works? Just curious . . .
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"This works because you are finishing simplifying a complex fraction. The problem with this video is that you are showing students how to "do" math and not "think" it. Why not show "straight across" division of numerator by numerator and denominator by denominator? Why not show that you can get common denominators and then simply divide the numerators? I taught this method 17 years ago and have recently moved on to a "multiple method" approach. This approach is "academically sound," yet it's also academically incomplete. Check this out for how it might look:
https://docs.google.com/file/d/0B6AnUSdDebMXc2dqcUR1SHBNT00/edit"