The more of this there is, the less you see. What is it?

A famous swimmer can swim downstream in a lake in exactly 40 minutes with the lake current.
He can swim upstream in that lake in exactly 60 minutes against the lake current.
The length of the lake is 2 km.

How long he can cover the distance of one side at a still lake with no current?

A man walked into a pub and went straight towards the Barman. He asked for a dirty martini from the Barman. The Barman thought something and then pulled out a pistol from his drawer and aimed it directly at the man. Why did he do that?

Using the clues below, what four numbers am I thinking of?

The sum of all the numbers is 31.
One number is odd.
The highest number minus the lowest number is 7.
If you subtract the middle two numbers, it equals two.
There are no duplicate numbers.

The person who makes it has no need for it. He who purchases it does not use it. The person who does use it does not know they are. What is it?

A and B have a certain number of chocolates with them. If B gives one chocolate to A, they will have an equal number of chocolates. But if A gives one chocolate to B, then A will be left with half the number of chocolates that B has.

Can you find out the number of chocolates they have right now?

What is black when you buy it, red when you use it, and gray when you throw it away?

"That Restaurant always remains crowded. This is the reason why nobody goes there".

Can you find a flaw in this statement?

What is the next number in the series?

15 29 56 108 208 ?

Can you find the missing number in the third row?
35 20 14
27 12 18
5 2 ?