Why is 6 afraid of 7?

What has six faces, but does not wear makeup, has twenty-one eyes, but cannot see? What is it?

Use the digits from 1 up to 9 and make 100.

Follow the rules.
=> Each digit should be used only once.
=> You can only use addition.
=> For making a number, two single digits can be combined (for example, 4 and 2 can be combined to form 42 or 24)
=> A fraction can also be made by combining the two single digits (for example, 4 and 2 can be combined to form 4/2 or 2/4)

Question: how can we do this?

What number comes next in the series?

5 15 5 18 5 24 14 20 _

I never stop running even when I standstill. If I am formed by joining two identical bodies together, can you guess who I am?

Always in you, Sometimes on you;

If I surround you, I can kill you.

What am I?

How many times can you subtract the number two from the number fifty?

As easy as you can get into me, it is as hard to get out of me.

Do you know what I am?

The square root of number 121 is "11". What is the square root of the number "12345678987654321."?

The day before yesterday I was 25 and the next year I will be 28. This is true only one day in a year. What day is my birthday?