Math Is Fun Forum

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

Jai Ganesh

Administrator

Registered: 2005-06-28

Posts: 52,105

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).

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It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

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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. //

phrontister

Real Member

From: The Land of Tomorrow

Registered: 2009-07-12

Posts: 4,910

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

Hi Nickm62388;

Here are steps I generally use for imperial subtractions.

Both problems contain components whose values are greater than those of their counterparts from which they are subtracted – just to make life difficult!

Problem #1 (lengths):
Imperial lengths: 1 foot (') = 12 inches (").

You could also use a formula to obtain the result of the subtraction in eighths of an inch by deducting the second length from the first (both in eighths of an inch), like this:

Then convert the result to feet ('), inches (") and eighths...

Problem #2 (angles):
Imperial angles: 1 degree (°) = 60 minutes (') and 1 minute (') = 60 seconds (").

You could also use a formula to obtain the result of the subtraction in seconds by deducting the second angle from the first (both in seconds), like this:

Then convert the result to degrees (°), minutes (') and seconds (")...

I hope that helps!

Last edited by phrontister (2025-10-08 00:48:57)

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hearpary

Member

Registered: 2022-06-27

Posts: 2

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

Isn't it necessary to convert to the metric system first? I mean from inches to cm.

Bob

Administrator

Registered: 2010-06-20

Posts: 10,803

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

hi hearpary

Welcome to the forum.

You could do that and get the same answers.

But, looking at the question, it is more an exercise in subtracting fractions, than a question about imperial measures.  Because the conversion multiplier for inches into cm isn't an exact value, the metric answer wouldn't convert back nicely to eighths of an inch.

When we do a number subtraction you may have to use one of these tricks:

71 - 46 = 60 + 11 = 46 so you can do 11 take 6. 

Some people use equal addition to do this  71 - 46 = 70 + 11 - (40 +10 + 6)

Either method works.  But, for degree measures you need 60ths not 10ths.  So the second question practises this.

You'd face a similar problem if you had to subtract hours and minutes.

Bob

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