Here’s your chance…The secret to learning percentages

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By Mike O’Hern, Center Director of Mathnasium of West Knoxville

 

June2013OHernYou probably have a pretty good idea of what percentage is, at least in some circumstances.  When there’s a sale for 20% off, you know that your $100 item will be $80, right?  Or at least you know that an 80% chance of rain means it’s likely you’ll get wet, and a 10% chance means you might get the motorcycle out.

But your child may not yet really have a grasp on the concept, and if he takes the traditional route to learning percentages it may be quite a long time before he makes sense of it.  But I’ve got students in 2nd and 3rd grade who can tell you what 5% of 250 is in their head, so let’s simplify it a bit and see if he can learn something new today!

It all starts with simply knowing what the word means.  PERCENT.  “Per” means “for each.”  Miles per gallon, for example, means how many miles can you drive for each gallon of gas you buy.  Dollars per hour means how many dollars you get for each hour you work.  “Cent” means one hundred.  There are one hundred cents in a dollar.  One hundred years in a CENTury.  Even the Roman numeral for one hundred is C, for cent!  Percent: For Each Hundred.

At this point you need to bring it to life for your student.  If she’s a gymnast, make it about 100 back handsprings.  If he’s a ball player, it’s about 100 pitches or hits.  If she’s a piano player, it’s about 100 minutes of practice.  You get the idea.

 

“It all starts with simply knowing what the word means.  PERCENT.  ‘Per’ means ‘for each.’”

 

So, now if I told you I would give you $6 for every 100 daisies you pick, how much would I owe you if you picked 100 daisies?  Simple enough: $6.  What if you got busy and picked 200?  Well, you get $6 for each 100 picked, so you get $6 for the first hundred and $6 more for the second hundred.  That’s $12!  But the next day you weren’t feeling so well, so you only picked 50.  Usually the child gets this pretty quickly, but if not, remind him that 50 is only half of 100, so he gets only half of the money: $3.  Finally, the next day you’re determined to make as much as you can and you pick 250 daisies.  Great!  $6 for the first hundred, $6 for the second hundred, and $3 for the final 50.  Add them all up and you have yourself $15!

Now you’re ready to take the same concept and make it about percents.  For each hundred.  Just like the $6 for each hundred daisies, you get five cobs of corn for every hundred that you pick!  You get 5% of the corn you pick!  So if you pick 100, how many do you get?  But now it gets a little trickier for the young student if she only picks 50.  We’ll have to talk about half of an odd number.

If we had five cookies, how could we share them fairly?  Don’t just tell him – let your child figure it out!  You might have to suggest, “you get one, I get one, you get another, I get another, but what can we do about the last one?”  Yes, you break it in half, so how many do we each get?  Two and a half.  Perfect.

So what’s 5% of 350?  350 = 100 + 100 + 100 + 50.  So, we get 5 + 5 + 5 + 2 1/2 = 17 1/2 !

Sure, more complicated numbers will have to wait until we know about decimals, but you have now nailed down the concept of percents, which will help when they get more complicated!

It’s fun to learn something new, isn’t it?  Maybe next issue we can start talking about “out of”…

Mike O’Hern, Center Director of Mathnasium of West Knoxville, earned his Bachelor’s Degree in Metallurgical Engineering at the University of Tennessee, Knoxville in 1988. He pursued graduate studies in Materials Science & Engineering while on the Research Staff at Oak Ridge National Laboratory. Mike has had a life-long love of mathematics and teaching, and feels that math is not about learning to be ready for the next math class – it’s about learning to think.

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