Can you solve this amazing hard number series problem?
7, 8, 10, 12, 16, 18 ?

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 certain street contains 100 buildings. They are numbered from 1 to 100. How many 9's are used in these numbers?

Find the next number in the series?
2, 12, 36, 80, 150, 252, 392, _ ?

By including only four matchsticks in below picture, you have to make "Four Triangles And Two Squares"

Using mathematical symbols like +, -, and x in order to make the equations correct. Replace # with the above-given symbols.

9 # 8 # 7 # 6 # 5 # 4 = 91

The answer I give is yes, but what I mean is no. What was the question?

I was born in a small house and I live in it all alone. No windows and no doors have been assigned to my house. The only way I can go out is by breaking through the walls of my house.

Who am I?

Count the number of squares in the picture below.

I know a ten-letter word in the English language which can be typed using only the top rows of the computer keyboard.