# Thread: How long is a piece of string?

1. ## How long is a piece of string?

A cylinder 90 cm high has a circumference of 20 cm. A string makes exactly 6 complete turns round the cylinder while its two ends touch the cylinder's top and bottom. How long is the string in cm?

2. ## Re: How long is a piece of string?

<span style="background-color: #FFFF00; color: #000000; font-weight: bold"><font color=yellow>Going for the quick answer, I get string length = 150 cm. I'll provide more detail when I get home</font color=yellow></span hi>

3. ## Re: How long is a piece of string?

That's what I get, Chris.
An old joke suddenly came to mind:
Q Are you a tatty piece of string?
A No, I'm a frayed knot!
Sorry.

4. ## Re: How long is a piece of string?

Sorry.. got home lastnight, and didn't touch the computer <img src=/S/sad.gif border=0 alt=sad width=15 height=15>. I'll get the detail later today.

5. ## Re: How long is a piece of string?

Talking of jokes ...

This reminds me of the classic question "How long is a piece of string?" BTW, we were actually asked this by a science teacher in year 9 (15 yrs old) on a pop quiz. You just had to put something down to get the mark - like "twice half its length" or "from one end to the other".

My preferred answer to this question is "No, he is not a piece of string, he is a man from China!"

6. ## Re: How long is a piece of string?

Yes, but how high is his brother.

7. ## Re: How long is a piece of string?

How High is a mountain in China, isn't it?

Alan

8. ## Re: How long is a piece of string?

Not sure about the "brother" thing but I was able to solve the puzzle by flattening the cylinder...

9. ## Re: How long is a piece of string?

Interseting the different mental approaches. I envisaged a process akin to "inking" the string then rolling the cylinger down a piece of paper. This would produce a line of ink, angled down and across the page. This line would cover a downward displacement of 6 x cylinder circumference (6 revolutions of the cylinder as it travelled down the page) and a lateral displacement equal to the cylinder height. So again, the length of the line (string) is that of the hypotenuse of the right triangle so defined.

Alan

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