My Math Forum Division example in Pre-Algebra book seems confusing

 Elementary Math Fractions, Percentages, Word Problems, Equations, Inequations, Factorization, Expansion

 October 26th, 2014, 01:05 AM #1 Newbie   Joined: Oct 2014 From: Washington Posts: 2 Thanks: 0 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: Code:  _1__ 37|543 -37_ 173 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.
 October 26th, 2014, 01:37 AM #2 Senior Member     Joined: Nov 2010 From: Indonesia Posts: 2,001 Thanks: 132 Math Focus: Trigonometry $\displaystyle 37\times4=148$, which is less than 173. $\displaystyle 37\times5=185$, which is more than 173, thus 5 is too large. Thanks from topsquark and Equals
 October 27th, 2014, 02:12 AM #3 Senior Member   Joined: Apr 2014 From: Glasgow Posts: 2,155 Thanks: 731 Math Focus: Physics, mathematical modelling, numerical and computational solutions 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. Thanks from topsquark and Equals

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