How long is it?
A string is wound Symmetrically around a circular rod. The string goes exactly four times around the rod. The circumference of the rod is 4cm and the length is 12cm. Find out the length of the string:
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The answer is 20.
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3 solutions
Another way to do this is to take a fat pencil which is 4cm thick. Then we must mark 12 cm on it. Then mark 3 lines which are 3cm apart from each other. Then with the help of a cellotape, attach a piece of string to the bottom. Then wind it four times around the pencil ending at the very top. Each loop should cross one of the lines which you drew. Then unwind the string after marking the point of intersection of the string with the top. Remove it from the pencil. Measure, the length of the string used. If your measurements are precise, you would get the answer as 20 cm. Did you like it Rishab.
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Hmmm, nice approach now words you are surely a good thinker hats of sir
Rishab, my answer is a different from yours. However nice approach.
I consider, the rod and a paper sheet which is rolled.
Then if we unfold a paper, then we get a figure which is somewhat this:-
(Sorry, for the fact that it is not drawn with scale. I made it in paint)
The smaller side is 1 2 c m long. And the larger side is 1 6 c m long. Now, when we divide the larger part into 4 equal parts, then each small part will be equal to 4 c m . Now join the end part of first division with the top edge of its adjacent side.
It forms a right angled triangle. Now, using Pythagoras' theorem,
4 1 length of string = [ 3 2 + 4 2 ] 2 1 = [ 9 + 1 6 ] 2 1 = 2 5 2 1 = 5
Therefore, length of the string is 5 × 4 = 2 0 c m
That's also one of the method, nice try.
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Thanks dude
Hi, try out my new problem " this is not possible mathematically......"
The string is wound around a cylinder then it will be greater than the length of the cylinder. Now each time when the string is rolled around the cylinder it will cover the distance of half of the circumference of the cylinder. Then, it will be 1/2 * 4 = 2, 12 + 2 * 4 = 20cm because it is rolled 4 times around the cylinder.
👍🎉, correctly answered. There are many solutions but, all lead to one and only one answer and that is 20
Ok, If you do not get the answer then here is a huge h i n t :