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October 26th, 2014, 01:05 AM   #1
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Exclamation Division example in Pre-Algebra book seems confusing

Hello guys and girls.

I purchased a used copy of Pre-Algebra Demystified, 1st edition from the bookstore recently in an effort to build myself a solid foundation for math success. I have quite a lot of catching up to do, and to be honest I'm not having an easy time with division.

My book provides an example that left me confused:
Divide 543 by 37

I get to a point where the problem looks similar to the following:
The next step says to divide 3 into 17. Well, if you multiply 3 by 5, you get the closest you can get to 17 without going over. I would think the next number in the quotient should be the number 5. The book says, "Note: The answer 5 is too large, so try 4."

How is that determined? I am mystified as to why the book's author would exclude the reasoning for the statement.
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October 26th, 2014, 01:37 AM   #2
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$\displaystyle 37\times4=148$, which is less than 173.
$\displaystyle 37\times5=185$, which is more than 173, thus 5 is too large.
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October 27th, 2014, 02:12 AM   #3
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I imagine many people don't know their 37 times table, so the book is suggesting a subtle trick where you try looking only at the tens digit first. Monox's result is the best one, but can be tricky to do in your head.
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