Climbing ropes

Given how much this 50 m rope weighs, can you find how much a 100 m rope weighs, if the thickness is different?
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Problem



Climbers use ropes of different diameters.

A 50 m rope which is 9 mm in diameter weighs about 2.7kg.

Roughly what would a 100 m rope of the same material, but of diameter 11 mm weigh?

This problem is taken from the World Mathematics Championships