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'Air Routes' printed from http://nrich.maths.org/
London is situated at longitude $0^o$, latitude $52^o$ North and Cape Town at longitude $18^o$ East, latitude $34^o$ South. Taking the earth to be a sphere with unit radius (and ultimately scaling by 6367 kilometres for the radius of the earth) work out coordinates for both places, then find the angle LOC where L represents London, O the centre of the earth and C Cape Town. Hence find the
distance on the surface of the earth between the two places. If a plane flies at an altitude of 6 kilometres and the journey takes 11 hours what is the average speed?
[You might also like to try the problems 'Over The Pole',
which is a little simpler, and 'Flight Path'
which is similar to 'Air Routes' but the method of solution given there is a bit different. ]