What goes up but never comes down?

What does this mathematical rebus means ?

John was running from 40 thieves. John has got 3 gold boxes which weigh as 4kg, 2kg, and 1kg respectively. A witty man asked John to stay with him for seven days in exchange for 1kg gold per day. John needs to stay there for seven days and also do not want to give the witty man any advance. How can John pay for his seven days stay?

A new Engineering building containing 100 offices had just been completed. John was hired to paint the numbers 1 to 100 on the doors. How many times will John have to paint the number nine (9)?

A man stands on one side of a river, his dog on the other. The man calls his dog, who immediately crosses the river without getting wet and without using a bridge or a boat. How did the dog do it?

You walk into a room that contains a match, a kerosene lamp, a candle and a fireplace. What would you light first?

Until it is measured, not known. Yet how you miss it when it has gone. What is it?

It comprises roots which nobody sees,
Much taller than those trees,
Up and up it goes,
Still it never grows?

I have a big mouth and I am also quite loud! I am NOT a gossip but I do get involved with everyone's dirty business.

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?