What is the longest word in the dictionary?

We have four gears with below features=> Both Gear A and D has 60 teeth=> Gear B has 40 teeth=> Gear C has 20 teeth=> Every two minutes, Gear B makes 25 full turns.What is the relative speed of Gear A and Gear B?

If 21x = 79x, what is the value of x?

I am a five-letter word under you,
Remove the first letter and I am above you,
Remove the second as well and I am around you.

Who am I?

I am lying and I always lie. Tell me whether I am lying or telling the truth.

what does this picture(rebus) riddle means ?

A shepherd had 18 sheep, out of which, all but ten died.

Can you tell us how many sheep was he left with?

A man is looking at a photograph of someone. His friend asks who it is. The man replies, “Brothers and sisters, I have none. But that man’s father is my father’s son.” Who was in the photograph?

John is the son of Jacob.
So,
Jacob is the_____of John's father?

Use only one mathematical symbol and all numbers (0-9) to get a sum of 99