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#1 2021-06-30 09:38:55

Nickm62388
Member
Registered: 2021-06-30
Posts: 2

Cannot find formula or solution to get answer for feet/inch addition

I have the answer to these two problems, but cannot figure out how they were got, and cannot find a formula or anything online to get the answer please help


Problem #1

   17ft. 7 1/2in.
-  14ft. 9 7/8in.

=??????????

Problem #2

   59degrees 37’ 18”
-   40 degrees 43’ 22”

=????? I don’t understand how you subtract something with degrees and feet and inches

Again I have the answers from the answer key but no idea how the answers came to be…

Please help

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#2 2021-06-30 12:04:59

ganesh
Administrator
Registered: 2005-06-28
Posts: 33,862

Re: Cannot find formula or solution to get answer for feet/inch addition

Hi Nickm62388,

Welcome to the forum!

Please see the links:

US Standard Lengths.

Degrees (Angles).

Minute (angles).

Second (angles).


It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi. 

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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#3 2021-06-30 12:23:39

Nickm62388
Member
Registered: 2021-06-30
Posts: 2

Re: Cannot find formula or solution to get answer for feet/inch addition

I appreciate the links, but with the equations I listed. I don’t see how exactly they relate or help answer them with the links. hmm//

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#4 2021-06-30 17:29:19

phrontister
Real Member
From: The Land of Tomorrow
Registered: 2009-07-12
Posts: 4,690

Re: Cannot find formula or solution to get answer for feet/inch addition

The image shows my solution technique for the imperial length subtraction problem.

There are 2 main difficulties with this subtraction exercise:
(a) unfamiliarity with imperial length measurements (but see ganesh's link);
(b) that the inches & fraction components in the first length are less than their counterparts in the second length.

My approach is to start with the following steps on the first length:
1. convert the fraction to the Least Common Denominator (LCD);
2. adjust the values of the fraction and inches components (in that order) to make both of them greater than those in the second length.

Then the last step of subtraction to obtain the answer is an easy one.

Btw, the 'take' and 'add' terminology that I used is like 'borrow' and 'pay', now aka 'regrouping', and is how I've always understood that concept.

Also, I've used symbols ' and " instead of abbreviations 'ft' and 'in' respectively...a common notation practice for these imperial length units.

HE5wkvd.jpg

For a formulaic approach, you could convert both lengths to eighths of an inch, deduct the second from the first, and convert the result to feet, inches and eighths:

That last conversion from eighths is a bit tricky...

Edit:

I haven't done the second problem, but it looks like you'd use the same technique.

Last edited by phrontister (2021-07-22 12:25:08)


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