Can you convert the number zero(0) into a positive number using just one mathematical operator ?

I came first on earth but second on the heaven.
I also came twice in a week but found just once in a year.
I stay away from months but you can find me in February.

What am I?

Using Only Five 5's and any mathematical operator make sum as 37

A seven-year-old kid challenged his classmates that he can make the number one disappear by adding something to it.

How can he do that?

If you remove one from eleven, it becomes ten. If you remove one from nine, it becomes ten.

How is this possible?

I want to fill my bucket using both cold and hot water.
I have two taps for both cold and hot water. The hot water tap fills the bucket in exact 6 hours and the cold water tap fills the bucket in exact 4 hours.
I turn both of them simultaneously but I forgot to turn off another tap which removes the water out of the bucket. This tap can empty the bucket in 12 hours.

How Long will it take to fill the bucket?

A pond had 60 fish, out of which, all but 20 died.
How many fishes are now present in that pond?

John replied, when asked how old he was. In 2 years he will be twice as old as he was five years ago.' How old is he ?

A beggar on the street can make one cigarette out of every 6 cigarette butts he finds. After one whole day of searching and checking public ashtrays the beggar finds a total of 72 cigarette butts. How many cigarettes can he make and smoke from the butts he found?

You board a train. The train will have to enter a tunnel soon. You are claustrophobic. Which place is the best for you to sit?