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Easy - too easy

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Fergus Kyle

Joined: 03 Jun 2007
Posts: 291
Location: Burlington ON Canada

Posted: Sat Jun 23, 2007 6:30 pm Post subject: Easy - too easy

My old math teacher said " When it's easy, be wise, do it twice."



Example:

30c x 2 = 60,

minus 10%  (60-6=56),

56 + 32 = 86F



Do it in your head easy



Second time, I don't think so.

Cheers, Ferg

lm4(at)juno.com
Guest

Posted: Sun Jun 24, 2007 6:21 am Post subject: Easy - too easy

Hi Folks,

        Guess I missed most of this thread. Are we trying to mentally

convert Fahrenheit to Centigrade ? 



Larry Mac Donald

lm4(at)juno.com

Rochester N.Y.

Do not archive



On Sat, 23 Jun 2007 22:28:28 -0400 "Fergus Kyle" <VE3LVO(at)rac.ca> writes:

 	  Quote: 	
		   

 

 My old math teacher said " When it's easy, be wise, do it twice."

 

 Example:

 30c x 2 = 60,

 minus 10%  (60-6=56),

 56 + 32 = 86F

 Do it in your head easy
	


 Second time, I don't think so.

 Cheers, Ferg

Fergus Kyle

Joined: 03 Jun 2007
Posts: 291
Location: Burlington ON Canada

Posted: Sun Jun 24, 2007 7:18 am Post subject: Re: Easy - too easy

Right, Larry,

         Basically, the topic was an easy way to convert. However you can see the arithmatic  fialed and although the answer was correct, the math wasn't. I was just noting that the easier the arithmatic, the greater the need to do it twice.....

Cheers, Ferg

jrccea(at)bellsouth.net
Guest

Posted: Sun Jun 24, 2007 9:25 am Post subject: Easy - too easy

I'm afraid I miss the point.  This is indeed the easiest way to mentally 

convert from C to F, and is so quick that you can do it as fast as you say 

it.

JimC

---

Float Flyr

Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland

Posted: Sun Jun 24, 2007 10:36 am Post subject: Easy - too easy

The first time I've seen it expressed that way



Noel

VO1 PL



[quote] --

_________________
Noel Loveys
Kitfox III-A
Aerocet 1100 Floats

klwerner(at)comcast.net
Guest

Posted: Sun Jun 24, 2007 12:50 pm Post subject: Easy - too easy

60 - 6  *IS NOT*  56,   but rather equals 54,  no???

 And 56 + 32 = 88,  and not 86.

  

 But it looks like two wrongs can  make things right after all.....

 [quote]>    Example:

[quote] 30c x 2 = 60,

 minus 10%  (60-6=56),

 56 +    32 = 86F

 

 Do it in your head easy

 

 Second    time, I don't think so.

 Cheers, Ferg[b]

jrccea(at)bellsouth.net
Guest

Posted: Sun Jun 24, 2007 1:11 pm Post subject: Easy - too easy

It's the way I've always done it.

JimC

---

Float Flyr

Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland

Posted: Sun Jun 24, 2007 2:00 pm Post subject: Easy - too easy

(9/5C) +32=F



(F-32)(5/9)=C



That's the way I was shown... A bit bulky for doing without paper or a

calculator.  Yours is definitely easier.  I tried it on -40C =-40F,  0C=32F,

20C=68F, 100C 12F all worked correctly.



Noel



[quote] --

_________________
Noel Loveys
Kitfox III-A
Aerocet 1100 Floats

s_korney(at)hotmail.com
Guest

Posted: Sun Jun 24, 2007 4:38 pm Post subject: Easy - too easy

Now try it backwards... to get back to Cent.

Best... Steve



----Original Message Follows----

From: "Noel Loveys" <noelloveys(at)yahoo.ca>

Reply-To: engines-list(at)matronics.com

To: <engines-list(at)matronics.com>

Subject: RE: Easy - too easy

Date: Sun, 24 Jun 2007 19:29:33 -0230






(9/5C) +32=F



(F-32)(5/9)=C



That's the way I was shown... A bit bulky for doing without paper or a

calculator.  Yours is definitely easier.  I tried it on -40C =-40F,  0C=32F,

20C=68F, 100C 12F all worked correctly.



Noel



 > --

apilot2(at)gmail.com
Guest

Posted: Sun Jun 24, 2007 5:06 pm Post subject: Easy - too easy

One example will show it only gets you within 10%.

-40F=-40C

-40-32/2=-36 does not equal -40.



On 6/24/07, steve korney <s_korney(at)hotmail.com> wrote:

[quote] 

 Now try it backwards... to get back to Cent.

 Best... Steve



 ----Original Message Follows----

 From: "Noel Loveys" <noelloveys(at)yahoo.ca>

 Reply-To: engines-list(at)matronics.com

 To: <engines-list(at)matronics.com>

 Subject: RE: Easy - too easy

 Date: Sun, 24 Jun 2007 19:29:33 -0230



 



 (9/5C) +32=F



 (F-32)(5/9)=C



 That's the way I was shown... A bit bulky for doing without paper or a

 calculator.  Yours is definitely easier.  I tried it on -40C =-40F,  0C=32F,

 20C=68F, 100C 12F all worked correctly.



 Noel



  > --

jrccea(at)bellsouth.net
Guest

Posted: Sun Jun 24, 2007 5:22 pm Post subject: Easy - too easy

That's because it's exactly the same equation, just configured differently. 

9/5X is the same as 2X-2X/10.  Both equal 1.8X

JimC



---

longg(at)pjm.com
Guest

Posted: Sun Jun 24, 2007 5:39 pm Post subject: Easy - too easy

Rule of thumb is easiest. Double it and add 30. Normally accurate within

1-2 degrees. Opposite for converting back.



--

ElleryWeld(at)aol.com
Guest

Posted: Sun Jun 24, 2007 6:05 pm Post subject: Easy - too easy

I would think the easiest way to convert in either direction would be to use your flight computer  it works for me 

 

  Ellery in MAINE  

 

 do not archive

**************************************

 See what's free at http://www.aol.com.  [quote][b]

truflite(at)yahoo.com
Guest

Posted: Sun Jun 24, 2007 6:31 pm Post subject: Easy - too easy

Should read 2X-(2X/10)+ 32=F.  Math in brackets is

done first.  Hey, I do remember something from high

school. 



Dave



--- jrc <jrccea(at)bellsouth.net> wrote:



[quote] 

 <jrccea(at)bellsouth.net>

 

 That's because it's exactly the same equation, just

 configured differently. 

 9/5X is the same as 2X-2X/10.  Both equal 1.8X

 JimC

 

 ---

lm4(at)juno.com
Guest

Posted: Mon Jun 25, 2007 4:41 am Post subject: Easy - too easy

Thanks Ferg,

        That's an annoying little piece of arithmetic.  When it's 

not critical, and when I can accept an answer within 

2 or 3 degrees I use something I learned from a friend 

in Toronto. I simply take F. subtract 30 and divide by 2 to get C.

Or take C. double it and add 30. Works a lot of the time for me.



On Sun, 24 Jun 2007 08:18:26 -0700 "Fergus Kyle" <VE3LVO(at)rac.ca> writes:

 	  Quote: 	
		   

 

 Right, Larry,

          Basically, the topic was an easy way to convert. However 

 you can see the arithmatic  fialed and although the answer was 

 correct, the math wasn't. I was just noting that the easier the 

 arithmatic, the greater the need to do it twice.....

 Cheers, Ferg

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=120344#120344

jrccea(at)bellsouth.net
Guest

Posted: Mon Jun 25, 2007 8:22 am Post subject: Easy - too easy

Lets try that, using 100C (the boiling point of water).

2*100+30 30F

The correct answer is 212F

The error is 28F.

Is that close enough? (it's slightly more than 1-2 degrees)



The exact answer requires only one more substraction.



JimC

---

jrccea(at)bellsouth.net
Guest

Posted: Mon Jun 25, 2007 8:28 am Post subject: Easy - too easy

The brackets are optional, not required.

2X-(2X/10) is the same as 2(X-X/10) is the same as 2X-2X/10 is the same as 

2X(1-0.1) is the same as 1.8X

Personally, I think its easiest to just do the thing in your head.  

JimC



---

peter(at)us-eurolink.co.u
Guest

Posted: Mon Jun 25, 2007 9:19 am Post subject: Easy - too easy

Let's try the UK version:



C to F = double it, less 10%, add 32

Eg 100C x 2 = 200 - 10% = 180 + 32 = 212F

That's pretty close for me!



F to C slightly less accurate

F less 32, add 10%, halve it

Eg 212 - 32 = 180, add 10% = 198, halve it = 99C

Still good enough for me!



Kind regards

Peter Grant - UK Sportcruiser #4 (waiting)

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rv8vator(at)comcast.net
Guest

Posted: Tue Jun 26, 2007 7:10 am Post subject: Easy - too easy

You guys are arguing from the standpoint that the formula is an

approximation.  It is an exact conversion, Why?



Because between freezing and boiling there are 100 Centigrade degrees and

180 Fahrenheit degrees. The ratio is 9/5. Centigrade freezing starts at "0"

Fahrenheit starts at 32.



So lets convert 20° C to Fahrenheit .



20 x 9/5 = 36 (The number of Fahrenheit degrees) since Fahrenheit begins at

32° adding 32 to 36 gives us 68°F.



Doubling 20 and subtracting 10 percent is just an easier way than

multiplying by 9 and dividing by 5.



Martin Sobel

jrccea(at)bellsouth.net
Guest

Posted: Tue Jun 26, 2007 11:40 am Post subject: Easy - too easy

Ummh, no.  I think I specifically said that doubling less 10% was an exact 

conversion.  Some of the other guys prefer using approximations.  I agree 

with you.

JimC

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