If the distance between each degree of longitude at the equator is approx 111km, what is the approximate distance between the following coordinates:
90°N, 100°E; and
90°N, 30°W
If it helps, you can assume the earth is a perfect sphere, instead of a oblate spheroid.
Cookie for the first person to get it

P.S. Yes Stef, I did post this up on my FB as well, so you don't need to make any special mentions of that, or in fact this on FB either.