## Welcome to BrainDen.com - Brain Teasers Forum

 Welcome to BrainDen.com - Brain Teasers Forum. Like most online communities you must register to post in our community, but don't worry this is a simple free process. To be a part of BrainDen Forums you may create a new account or sign in if you already have an account. As a member you could start new topics, reply to others, subscribe to topics/forums to get automatic updates, get your own profile and make new friends. Of course, you can also enjoy our collection of amazing optical illusions and cool math games. If you like our site, you may support us by simply clicking Google "+1" or Facebook "Like" buttons at the top. If you have a website, we would appreciate a little link to BrainDen. Thanks and enjoy the Den :-)
Guest Message by DevFuse

# 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

4 replies to this topic

### #1 antel0pe

antel0pe

Newbie

• Members
• 14 posts

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?
• 0

### #2 bonanova

bonanova

bonanova

• Moderator
• 6160 posts
• Gender:Male
• Location:New York

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?

• 0

Vidi vici veni.

### #3 skca

skca

Newbie

• Members
• 2 posts

Posted 04 February 2014 - 10:21 AM   Best Answer

4.166% change in the length of the ruler
• 0

### #4 harey

harey

Junior Member

• Members
• 92 posts
• Gender:Male

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.

• 0

### #5 antel0pe

antel0pe

Newbie

• Members
• 14 posts

Posted 04 February 2014 - 11:27 PM

4.166% change in the length of the ruler

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.

• 0

#### 0 user(s) are reading this topic

0 members, 0 guests, 0 anonymous users