Brain Teasers
The String Around the Cylinder
A cylinder 48cm high has a circumference of 16cm. A string makes exactly 4 complete turns around the cylinder, while its two ends touch the cylinder's top and bottom (forming a spiral around the cylinder).
How long is the string in cm?
How long is the string in cm?
Hint
Pythagoras' theorem may help.Answer
80cm.Finding the length of the string is the same as finding the length of the hypotenuse of a triangle with a height of 48 cm and a base of 64 cm (16 x 4). Using Pythagoras' theorem, you get:
h^2 = 48^2 + 64^2
Solving, h = 80 cm.
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