No one wants to have it, but if one got it, he does not want to lose it. What is It?

When it's bad luck to meet a black cat?

Considering the below equation:

V + II - VI = 10
IV - X + VIII = 20
IV - VII + VI = 30

Then, I + II + III = ?

Two-person want to cross a river. Only one boat is present on the riverside that can carry only one person at a time.

However, they still manage to cross the river. How is it possible?

This is a famous paradox which has caused a great deal of argument and disbelief from many who cannot accept the correct answer. Four balls are placed in a hat. One is white, one is blue and the other two are red. The bag is shaken and someone draws two balls from the hat. He looks at the two balls and announces that at least one of them is red. What are the chances that the other ball he has drawn out is also red?

What does the following represent?

N N N N N N N

A A A A A A A

C C C C C C C

What happened when the wheel was invented?

12345 a famous South Indian actor
567 is a path in jumbled form
8 & 10 are same letters
9 is one among the first six alphabets.
WHO AM I?

There's one "sport" in which neither the spectators nor the participants know the score or the leader until the contest ends.

What is it?

Why do we preferably have round manhole covers and not square ones?