why number 8549176320 is one of a kind?

A Scientist was fifty years old in the year 2000 but he was forty years old in the year 2010. How can this be possible?

PS: It has a logical answer.

I know a nine-letter word having only one vowel.
Do you ?

Two old friends, Jack and Bill, meet after a long time.

Three kids
Jack: Hey, how are you, man?
Bill: Not bad, got married and I have three kids now.
Jack: That's awesome. How old are they?
Bill: The product of their ages is 72 and the sum of their ages is the same as your birth date.
Jack: Cool..But I still don't know.
Bill: My eldest kid just started taking piano lessons.
Jack: Oh, now I get it.

How old are Bill's kids?

If I remove one from eleven it becomes Ten and if I remove one from nine also becomes Ten. How?

Look at the below sequence of letters and tell us what the next letter should be:

O T T F F S S ?

What kind of band never plays music?

Can you count the number of squares in the given picture?

Forwards I am heavy, backward I am not. What am I?

Thirty friends were on a hiking trip when they decided to enjoy the bonfire. They assembled for it and agreed to play a game. For that, they divided themselves into five teams with seven members each, forming five rows.

How did they manage to achieve this formation?