Getting comfy with conversions

Recently, I had some fun with numbers on my WAGM Facebook page. Even though “everyone” has a phone in their hand or by their side these days, it’s still important to exercise our brains. So what I did was post my “word version” of the formula for converting Celsius to Fahrenheit, and then gave a temperature in Celsius for people to try to figure out. 

The actual formula can look daunting to some. It is degrees Fahrenheit (F) = (degrees Celsius (C) x 9/5) + 32, or F = (C x 9/5) + 32. So some years back, I came up with an easier-to-use way to use this formula that is also very easy to remember. I will explain it in long form, then give you the short, easy-to-remember version.

Take the temperature you hear in Celsius and double it. Take away (subtract) one-tenth of the doubled amount. Add 32. Now, here’s the short, easy-to-remember version:

 Double it, take away a tenth. Add 32.

Let’s do one together. The one I posted on my Facebook Page set C equal to 25.  So, based on my word version, you double 25. That gives you 50. Take away one-tenth of the doubled amount. This leaves you with 45. Add 32. This gives you 77, which is correct: 25 C = 77 F.

But what if the number were negative? No problem!  Let C = -20. Doubling that gives you -40. Take away one-tenth of the doubled amount. Here you must remember that when subtracting a negative number, it’s the same as adding. So -40 – (-4) gives you -36. Add 32 and you get -20 C = – 4 F.

So again, when you need to go from C to F, double it, take away a tenth, add 32. Works precisely and works every time.

Now remind me again why on earth  we are doing something that we’ll “never” have to do, since our phones can do it for us. Easy. To keep our minds limber. But there is an even more important reason. I have seen many students convinced that they aren’t good at math. And, unfortunately, they become convinced of this at a rather early age. BUT, if you show them that they can, in fact, do a handy conversion in their head, why, it can instantly turn the confidence switch from “off” to “on”!

So I would suggest doing a few of these with any young people in your life. Getting math confidence early is key.

Now we are going to go the other way, from F to C. This “word version” gets you very close, but, unlike my C to F “word version”, it does not give you the exact answer. Let’s do one. First, the formula. C = (F – 32) x 5/9. Here’s my word version to go from F to C. Subtract 32 from F. Cut the result in half. Add back one-tenth of that amount. Let’s do one together. Let F = 68. Subtract 32. This leaves 36. Cut that in half. That leave 18. Add back one-tenth of that total. That would be 18 + 1.8. 19.8. And indeed, 68 F = 20 C. While my word version of F to C gets you very close, my other one, to go from C to F gives you an exact answer.

It is worth practicing both of these with your kids. It’s like going to the gym, but for your brain! And again, I can’t overstate the importance of building confidence in math early.

There are few things more satisfying than seeing the light bulb go off when a student suddenly gets it.

I’d be keen to know if your family found these exercises helpful. Shoot me a line at tshapiro@wagmtv.com.

Since we are talking about conversions, let me give you a couple of handy ones if you happen to be heading to Canada. 

For snow, every 5 centimeters is 2 inches.

For rain, every 25 millimeters is 1 inch.

Take the wind speed you hear in kilometers per hour and multiply by 0.6 to get a close approximation to miles per hour. 

Lastly, and unrelated, with a few trees still holding their leaves, if you have never done it, stand next to a tree on the next blue sky day we have, and look up at the sky through the branches and the leaves.

Our brains need that kind of exercise, too.

Ted Shapiro holds the Broadcast Seal of Approval from both the American Meteorological Society and the National Weather Association. An Alexandria, Va. native, he has been chief meteorologist at WAGM-TV since 2006. Email him at tshapiro@wagmtv.com 

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