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

You may enter, but you may not come in. I have space, but no room. I have keys, but open no lock. What am I?

A man desired to get into his work building, however he had forgotten his code.
However, he did recollect five pieces of information
* Fifth number + Third number = 14
* The fourth number is one more than the second number.
* The first number is one less than twice the second number.
* The second number and the third number equals 10.
* The sum of all five numbers is 30.

What is the code ?

If nine thousand, nine hundred nine dollars is written as $9,909,
how should twelve thousand, twelve hundred twelve dollars be written?

You need to climb ten stairs. At every stair, you can either take one step up or you can jump two steps up.

In how many different ways you can climb 10 stairs?

Can you find out the total number of triangles in the given figure?

Find the next number in the sequence

1, 2, 6, 21, 88, __?

I am thinking of a five-digit number such that:
The first and last digits are the same, their submission is an even number and multiplication is an odd number and is equal to the fourth number. Subtract five from it and we obtain the second number. Then divide into exact halves and we get the 3rd number.

What number I am thinking of?

There is a place where if I stand up straight, I will still be considered sideways.

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?