Today's math lesson, courtesy of the VideoText program, cleared up what has always been one of math's mysterious mysteries - that mystifying "invert-and-multiply" rule.
If you want to divide 4/5 by 7/8, then you would think that "all you do is multipy 4/5 by 8/7". But how in the world did we get 8/7 out of 7/8?
4/5 divided by 7/8 means 4/5 / 7/8. We have to get a one at the bottom, to simplify this strange and complex fraction. So we multiply 7/8 by its reciprocal - 8/7 - to get a one.
Does anyone understand why
We must invert and multiply?
It's a simplification of a simple process. Anyone who's worked with fractions knows that when you multiply the bottom of a fraction by any number, you have to do the top, too! So we multiply 4/5 by 8/7 too - tada! The answer is 32/35.
This was such an exciting discovery I just had to share it with someone. So if you're out there in the cyberworld and you've always wondered why we "never reason why - just invert and multiply"...
are you excited too?
Wednesday, May 13, 2009
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