if you fold a piece of paper 103 times, the thickness of it will be larger than the observable universe. (which is 93 billion light-years)

The optimal number of moves needed to solve a Rubik's cube from any configuration is only 20.

If you have 23 people in a room, there is a 50% chance that at least two of them have the same birthday. If you put 70 people in, the probability jumps to 99.9%.

1 x 1 = 1

11 x 11 = 121

111 x 111 = 12321

1111 x 1111 = 1234321

etc.

No matter how often you multiply 90625 with itself, it will always have 90625 at the end.

90625

90625² = 8212890625

90625³ = 744293212890625

etc.

Suppose a drug test is 99% sensitive and 99% specific. That is, the test will produce 99% true positive results for drug users and 99% true negative results for non-drug users. Suppose that 0.5% of people are users of the drug. If a randomly selected individual tests positive, what is the probability that he is a user?

The answer is around 33.2%

Source:

Reddit