In the past month, the world has been gripped by a series of maths and logic puzzles that were originally set for children.
First came the parked car puzzle which was set as a test for primary school children in Hong Kong but many adults still found tricky to solve. Then came Cheryl's birthday, set for 15 to 16-year-olds in Singapore but seemingly impossible for anyone to solve. And finally this week came the rod and string conundrum which stumped 96 per cent of top maths students in the US when it first appeared back in the 1990s.
Because all have proved so popular, and many of you seem to have already solved the original three, we've pored through the records to find eight more puzzles to leave you chewing your pencil and pulling out your hair.
Let us know how you get on...
1. How to beat Roger Federer at Wimbledon
Thanks to a set of temporary magical powers you are in the final of the Wimbledon tennis championships up against seven-time winner Roger Federer. Your powers cannot last for the whole match and you must therefore choose the optimum time for them to run out. What is the score that gives you the maximum chance of winning?
You must rearrange these matchsticks so that the olive (that's the thing in the middle) is removed from the Martini glass. The olive must not be touched and you are only allowed to move two of the matchsticks. The Martini glass can be turned onto its left or right side, or even upside down, but must remain in the exact same shape.
None of the below images are the solution because the olive is still inside the glass or because the glass has taken a different form.