Need help with teaching when to multiply vs. divide in word problems...

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#1 Mommy7

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Posted 24 March 2010 - 09:29 AM

My ds is having trouble knowing *when* to multiply vs. divide.

Any ideas about how I can teach this concept? I'm not good at this.

#2 Debbie in OR

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Posted 24 March 2010 - 10:17 AM

I don't know if this will help your ds but it was helpful with mine. We taught them that multiplication is just repeated addition and division is repeated subtraction. So, now they look at the problems trying to decide if adding will get the answer or subtracting will. It's not fool-proof but more often than not, breaking it down to those basic processes makes it clear enough to finish the problem.

#3 Pata

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Posted 24 March 2010 - 10:27 AM

Singapore teaches multiplication as number of groups x number in each group = total number, division is the total number divided by the number of groups(or number in each group) = number in each group (or number of groups). So it's just a matter of figuring out the information your given, for example...

Lindsey spent \$84 on 7 towels. What was the cost of 1 towel?

You are given the total amount=\$84, the number of towels=7 and you want to find how much each cost. Using the above formulas, you can know that you need to use division to solve the problem because you have been given the total amount spent. Does that make sense? Hopefully I explained it clearly enough, sometimes the pregnancy fog gets in the way .

#4 MerryAtHope

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Posted 24 March 2010 - 11:58 AM

My ds is having trouble knowing *when* to multiply vs. divide.

Any ideas about how I can teach this concept? I'm not good at this.

Sometimes I present a simplified example to my kids that they can readily see. If the problem is something like, "Jim had \$4.75 to spend on candy, and each piece cost \$.37 cents, how many pieces can he buy?" Then I break it down and say, "Let's pretend he had \$1.00 and each piece costs \$.25." Usually they can see that he could buy 4, so then I ask them whether they divided \$1.00 by \$.25, or multiplied by \$.25 to get that answer. We write out what the equations would be. Then we swap out the numbers for the real numbers of the problem.

Another thing I do is present logic--Let's say they multiply \$4.75 by \$.37, and come up with 1.75 pieces. Does that make sense that he could only buy one complete piece of candy? Let's subract \$.37 from the \$4.75 he has--we can see that he has lots of money left for more candy. That answer doesn't make sense does it? So I teach them to question their answers to see if they could really work or not.

Merry :-)

#5 Mommy7

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Posted 27 March 2010 - 07:58 AM

Great ideas, everyone. Thanks!!!

Has anyone used the Math Tutor DVD's on word problems? I was wondering if listening to it would help *me* as well as my dc.