What happened when the wheel was invented?

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

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?

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

Keyboard words are not in alphabetical order, Why?

Assume there are approximately 5,000,000,000 (5 billion) people on Earth. What would you estimate to be the result, if you multiply together the number of fingers on every person's left hand? (For the purposes of this exercise, thumbs count as fingers, for five fingers per hand.) If you cannot estimate the number then try to guess how long the number would be.

What has many teeth, but cannot bite?

In particular commonwealth games, a female participant won silver and gold medals for a single event.

How can this be possible?

Can anyone tell me a word in the English dictionary which has a silent 'z'?

Five thieves looted a bank and they ran away in a car. The bank staff informed the police and they began the search of their car in their jeep. They found them on a road and chased them eventually catching them. The light that is used to fill the number plate was broken on the thieves' car. Also, the headlights of the jeep police were not working. How were the police able to catch the thieves then?