Maths Labyrinth: Dirty Pond

Answer: Alice – In the second race, after Alice has run 100m of her 110m we know that Bob will have run 90m of his 100m. Both of them will have 10m left and they are level on the tracks, so the faster runner (Alice) will do the last 10m quicker. She still wins.

“You are getting closer to the exit”


A single bacterium in a pond doubles every 5 minutes. It takes 1 hour until the pond is completely full of bacteria. If there had initially been two bacteria in the pond, each doubling every 5 minutes, how long would they have taken to fill it?

30 minutes

55 minutes

1 hour