Find The Next Number In The Sequence

30 10 15 13 0 16 -15 ?

What is the four-digit number in which the first digit is one-third the second, the third is the sum of the first two, and the last is three times the second?

What can you deduce from the following BrainBat?

CRY
LMKI

There is a box in which distinct numbered balls have been kept. You have to pick two balls randomly from the lot.

If someone is offering you a 2 to 1 odds that the numbers will be relatively prime, for example
If the balls you picked had the numbers 6 and 13, you lose $1.
If the balls you picked had the numbers 5 and 25, you win $2.

Will you accept that bet?

Count the number of triangles in the picture below:

There are forty elephants and they have forty-fore heads. How can this be possible?

There is something which is always coming but never arrives?

They are the five precious gems of an everyday sort and all can be found on a Tennis Court. Who are they?

When I go in I might cause pain. I cause you to spit and ask you not to swallow. I can fill your hole. What am I?

I ask Joseph to pick any 5 cards out of a deck with no Jokers.

He can inspect then shuffle the deck before picking any five cards. He picks out 5 cards then hands them to me (Jack can't see any of this). I look at the cards and I pick 1 card out and give it back to Joseph. I then arrange the other four cards in a special way, and give those 4 cards all face down, and in a neat pile, to Jack.

Jack looks at the 4 cards i gave him, and says out loud which card Joseph is holding (suit and number). How?

The solution uses pure logic, not sleight of hand. All Jack needs to know is the order of the cards and what is on their face, nothing more.