The Petri Dish Puzzle.

Brainteaser Answer 10:

12.59 pm

This little cheeky brainteaser depends on a tendency to over-think the question.
You really don’t need to consider the ins and outs of bacteria, half-life and decay; you just need to work backwards and use a little bit of common sense!

At 1 pm the dish is full. If bacteria doubles every minute, then one minute earlier, the dish must have been half full. Bob’s your uncle; the dish was half-full at 12.59 pm!