Cheryl's Birthday is too easy
Geometry
Level
3
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 its length is 12cm. Find the length of the string (in cm).
The answer is 20.
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first if we make it flat then it will appear as:
Here AD is the circumference, and DC is the length of rod.
As the string is wrapped around symmetrically therefore, DG=GF=FE=EC=3 CM
By Pythagoras theorem,
AG = 5 CM =HF=IE=JC
Therefore total length of string is equal to 20 cm