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Warped Ruler


Best Answer skca, 04 February 2014 - 10:21 AM

4.166% change in the length of the ruler Go to the full post


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#1 antel0pe

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Posted 02 February 2014 - 03:05 PM

A certain ruler, which is supposed to be 12 in long, is warped and is actually just 11 1/2 in. If you measure off 4 ft of string with this ruler, what is the percentage error in your measurement?
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#2 bonanova

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Posted 03 February 2014 - 03:15 PM

Sounds like a homework problem.

Percentages are nice - they are invariant to scale.

So here's a clue: what is the percentage change in the length of the ruler?


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#3 skca

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Posted 04 February 2014 - 10:21 AM   Best Answer

4.166% change in the length of the ruler
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#4 harey

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Posted 04 February 2014 - 02:08 PM

There might be a trap. Back to the secondary school for the definition of the measurement error.

 

I have rulers which are divided in cm and subdivided in 1/10 of cm.

If I tell you I mesured 2.4 cm, you assume the the value is between 2.35 and 2.45. Error in percentace=0.1/2.4*100

If I tell you I mesured 7.4 cm, you assume the the value is between 7.35 and 7.45. Error in percentace=0.1/7.4*100

 

I happen to have a curiosity of a ruler in inches. It's subdivisions are 6 (for 6 lines per inch or 12 cpi), 8 (for 8 lines per inch or 8 cpi) and 10 (for 10 cpi).

 

(Supposing this ruler shrinked by 1/24, I get a headache.)

 

If antelOpe has such a ruler, the error is 1/subdivison/4*100.


Edited by harey, 04 February 2014 - 02:10 PM.

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#5 antel0pe

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Posted 04 February 2014 - 11:27 PM

4.166% change in the length of the ruler

 

Yep, that's the answer.

 

 

There might be a trap. Back to the secondary school for the definition of the measurement error.

 

I have rulers which are divided in cm and subdivided in 1/10 of cm.

If I tell you I mesured 2.4 cm, you assume the the value is between 2.35 and 2.45. Error in percentace=0.1/2.4*100

If I tell you I mesured 7.4 cm, you assume the the value is between 7.35 and 7.45. Error in percentace=0.1/7.4*100

 

I happen to have a curiosity of a ruler in inches. It's subdivisions are 6 (for 6 lines per inch or 12 cpi), 8 (for 8 lines per inch or 8 cpi) and 10 (for 10 cpi).

 

(Supposing this ruler shrinked by 1/24, I get a headache.)

 

If antelOpe has such a ruler, the error is 1/subdivison/4*100.

 

Also thanks for the creative and enthusiastic approach, harey.


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