Division and two digit divisors

[AimeeM]

Any tricks for this? DD11 is having a tough time. Oh, she knows the steps well enough and CAN get the answer, but it's a tedious process and takes her f.o.r.e.v.e.r.

She hit the section review in MM6 and it has a few of these problems - she immediately got teary eyed and said "I remember these from CLE!"; it was her most dreaded task in CLE (and she doesn't dislike math, but HATES two digit divisor division problems!).

 

I know CLE taught a "trick" of rounding the divisor and then reconverting it its exact; even I found this unnecessarily complicated for the dyslexic child (who has working memory problems as it is). Anything else?

[Wee Pip]

Yes! Do a google search for Partial Quotient Division (you might find it under Partial Product Division too). Khan Academy has 2 vidoes and there are other insyruction sheets / demos online. My dd used this method for awhile and eventually settled on doing division the normal way. It helped her over the hurdle. Btw, she was just really slow at it for a long time -tends to think/process slowly, but is good with concepts.

[Mom-ninja.]

I also let my ds do Khan Academy.

 

For what it's worth, *I* don't like double digit divisors. :tongue_smilie:

 

What MM (in level 5) has you do is write down all the products. Example: if 23 is your divisor then to the side you take the extra time to write out 23x2=26, 23x4=92, etc. Then you can glance at the chart while doing the division.

 

My ds hates doing this step, but when he does it then it helps him.

[wapiti]

I know it's reviewed in MM5, because ds just did this. It involves making a little multiplication table for the divisor.

 

I'm much too lazy for that. My own personal trick: I start the "guessing" by covering the ones digit of the divisor and one digit of the part of the dividend that you are currently guessing on. So, if it's 13678 divided by 24, and your first guess is how much does 24 go into 136, I'd start by covering everything but the 13 and the 2 to make that guess. Maybe the guess will be too big or too small by one, but it's a place to start.

[Karen in CO]

We went over a lot of ways of doing this until my dd realized that basically a good guess is just as fast as any other method (and is a valid method). When she was learning, we worked through them together trying to get close to the right answer in the least amount of tries. It was a lot of work for both of us, but she was less frustrated to see that I didn't get the right answer the first time too. Now, she is much faster than I am and the longer divisions like this are some of her favorite calculations. I think that in the long run, writing out all of the multiples of the divisor gets in the way of the division and slows you down.

[Ray]

Well if I did this right the attachment shows a drawing done in 'paint', using borrowed ideas. The example is 180/12 where one sees what 180 and 12 look like when using dots and boxes. This works off of how we write numbers using place value, hundreds,tens,ones etc.

Not so much a 'trick' to speed up computations, but a 'trick' to spark insight;)

Edited October 1, 2012 by Ray