Jack have ten pairs of black socks, eight pairs of white socks and seven pairs of green socks. Everything is mixed in a draw. As there is no light he were not able to identify the colour of the socks. How many of the socks did he want to take to match one pair
How many points are there on the globe where, by walking one mile south, then one mile east and then one mile north, you would reach the place where you started?