Solution:

It can be done as shown below.

Solution:

There are multiple solutions to the brain teaser.

1) 11+13+3! = 30
2) 11.5+5.5+13 = 30
3) 11+13+6(rotating 9)... my favorite.

Solution:

Felice & Nicolas.

The number corresponding to the atomic number of the elements.
26-3-58 (FE-li-ce) =>Felice
28-27-57-16(Ni-co-la-s) => Nicolas.

Also explained in the video.

Solution:

It can be done as shown below.

Solution:

Mark Benson '?' = question MARK, so the note on the door reads 'Question Mark Crimson broke your window.'

Solution:

The mathematician made a small fence around himself and declared himself to be on the outside.

Solution:

We can calculate out how many days there will be for the 13th on each month if we count from the beginning of the year (January 1). Then we divide total days by 7 to get the remainders. We also need to consider the leap year. Through the whole year we had all kinds of remainders, from 0 to 6. The minimum of occurence for all the unique remainders was 1. It means that we have at least one Friday on 13th. In a regular year, the best chance you can get 3 Fridays on 13th, which are in February, March and December because the remainders of these 3 months are 2. In a leap year, the best chance you also can get 3 Fridays on 13th, which are in January, April and July because the remainders of these 3 months are 6.

Solution:

Only twenty-three people need be in the room, a surprisingly small number. The probability that there will not be two matching birthdays is then, ignoring leap years, 365x364x363x...x343/365 over 23 which is approximately 0.493. this is less than half, and therefore the probability that a pair occurs is greater than 50-50. With as few as fourteen people in the room the chances are better than 50-50 that a pair will have birthdays on the same day or on consecutive days.

Solution:

What goes up must come down.

Solution:

1:45

The man gave away a total of 25 cents. He divided it between two people. Therefore, he gave a quarter to two