Some friends sat in a circle. Each had a whole number of dollars. The first had $1 more than the second, who had $1 more than the third, and so on. The first gave $1 to the second, who gave $2 to the third, and so on, each giving $1 more than s/he received, as [...]

A bag contains either a white ball or a black ball, and each case is equally likely. A white ball is added. You now randomly take a ball from the bag. If it is white, what is the probability that the remaining ball is white?

I’m not sure if this has been posted before.

What are the last N digits of 9^(9^(9^9))? That’s a power tower of nines.

Make N as large as you can. Personally, I’m not going to aim beyond N = 8 as far too much work would be involved.

I’ve discussed the maths you need in my last post. You will need to use a 9+ [...]