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Re: mental math, school, and making change
Posted By: Wolfspirit, on host 64.229.205.211
Date: Monday, August 27, 2001, at 08:19:20
In Reply To: Re: Visualization and mental math posted by koalamom on Friday, August 17, 2001, at 19:36:00:

> I think it has to do with being a concrete thinker vs being an abstract thinker. We concrete thinkers need to visualize THINGS. The abstract thinkers like Wes don't. Apparently. I don't really get how they do it either.
> [...]

> I got by in school with A's & B's because I was a pretty diligent student and could apply/recognize (on paper) some/most of the concepts. But I have no natural talent or intuition for it.
>
> Sometimes the way math was taught, made it harder.
>

Sometimes I imagine that that's the main problem: the way that math is taught. So much of the physical nature of the universe -- the intimate relationship between things -- requires an understanding of mathematics. Nature itself reveals a love of math on a profoundly intuitive level... in the way that leaves branch out and spiral regularly around a tree trunk... in the way that water molecules align snowflakes into six-sided hexagrams... in the tessellation of the honeycombs of bees. God's world is filled with a symphony of dancing numeric relationships. And yet the way we're taught math is often so dry and dead and brute force. Sure, you need the brute force method for some things, like memorizing basic multiplication tables. But without correlating abstract mathematical concepts to real-world concepts, students never develop an "intuitive feel" that the math they're learning has any relevance to the world or to their own lives.


> Having said all this, I still would not consider myself *bad* at math (just bad at *mental* math. I had a garage sale once and broke out in a cold sweat every time I had to make change, finally ended up working things out with a pencil and paper while my customers looked on in disbelief..boy, that was embarrassing..)
>

I can understand that feeling. How dare they look down on you! ;) Customers today are sooooo spoiled by those electronic cash register thingies, they think giving change is instantaneous, don't they? But truth to tell, making change is fairly easy if you know a simple trick. Basically, the trick is rounding the item sale price upwards and additively, to the nearest quarter and then nearest dollar, until you 'match' the amount that the customer has handed you. (The only reason this comes to mind is because I once worked in a Greek drycleaner's with no calculator nor register.)

Suppose at the garage sale the customer has selected a bunch of items totalling $13.35. She gives you a twenty; you need to make change. Mentally keeping the $13.35 in mind, do the following: First, pick up a nickel and a dime (15¢) to round the mental amount up to $13.50. Then add two quarters (50¢) to round to $14.00. Then add a dollar and a five ($1+$5) to sum the total to $20. The beauty of this method is that you don't even need to know what the total amount of the change is -- just sum the difference upwards, starting from the sale price until you reach the amount given by the customer, and the amount in your hand will be the correct change. Pretty neat, or at least I thought so.

Question. How many Rinkies actually learned this handy cashier's-change method in school? I certainly didn't. How about the cashier's etiquette of placing the coins in the client's hand first, then handing over the paper bills? (Doing it the other way will make the coins slide off the bill and drop on the floor). I never learnt about that either. But I *did* have an amazing algebra teacher in Secondaire III (Grade 9) who taught a trick to quickly calculate the correct tip to leave (for waitors/waitresses) BEFORE taxes on a restaurant meal. Mrs. Campbell was one great math teacher.

Wolfspirit

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