Puzzle for Today
Puzzle No. 501 鈥� Thursday 13 June
Heather and Dylan are sheep. It takes a shepherd 3 minutes to shear Heather's fleece. Dylan, being a sizeable ram, is twice as wide as Heather. Assuming, as all good scientists do, that all animals are spherical, how long should it take the shepherd to shear Dylan?
Today’s #PuzzleForToday has been set by Dr Geoff Evatt, School of Mathematics, University of Manchester
Click here for the answer
12 minutes. This is because the shearing is related to the surface area of the sheep - the more area to cut, the longer it takes. The surface area of a sphere (which we take to be the shape of a sheep) is proportional to the square of its radius. And so with Dylan being twice as wide as Heather, his surface area is (2 squared) 4 times the surface area of Heather. It thus takes 4 times as long to shear Dylan than it does Heather, namely 12 minutes. (This is highly idealised, especially as the real Heather only has three legs and hates the shearing process, and the real Dylan is so massive (and, technically speaking, a Whether) that shearing him is utterly exhausting. In reality I am pleased if I have sheared either of them within 20 minutes!).
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