Blog posts with problems to get your brain going! You get a new problem every fortnight and the solutions are published later.

If you want the problems delivered to your inbox be sure to subscribe to the Problems newsletter.

The next problem is scheduled for late May.

_{You may notice some problems are missing... I'm still migrating articles from my old blog.}

Please help me identify these 100 light bulbs by turning ON and OFF their switches.

This problem is a step up from Problem #028 - hidden key. Can you tackle this one?

There is a key hidden in one of three boxes and each box has a coin on top of it. Can you use the coins to let your friend know where the key is hiding?

Some people are standing quiet in a line, each person with a hat that has one of two colours. How many people can guess their colour correctly?

This post's problem is a really interesting problem I solved two times. The first time I solved it I failed to prove exactly how it works... then some years later I remembered the problem statement and was able to solve it properly. Let's see how you do!