When NASA first decided to put a man on the Moon they had a problem: once the Apollo spacecraft was in flight, they would not be able to observe its exact location and neither would they be able to predict it using physics. How could they send astronauts to the Moon if they didn't know where they were? An ingenious mathematician came up with an answer.

Dengue fever does the opposite of what you might expect. Unlike for many diseases, if you've had this tropical virus and recovered, you might be worse off, as a second exposure to the dengue virus can be life threatening. So keeping track of the strains of the diseases is an important problem which can be solved with the help of a little randomness.