How many sides does a circle have?

The centre of the third figure is empty. What digit should fit inside?

People make me, save me, change me, raise me. What am I?

Bopanna was working on a murder case when he received a message about the location of the murder weapon.
The message was encrypted as below.

"deb mitciv eht edisni neddih si nopaew redrum ehT"

Tell me the location of the murder weapon.

A boy collects white seashells from the sea and brings them home every night. When he has enough of them, he decides to sell them to a trader.

The trader is ready to buy the shells and he asks the boy about the quantity. At this, the boy starts calculating. He has a giant box that contains 3 mini boxes. Two of them have another mini box inside. If the giant box can hold 50 shells, how many brown shells can he sell to the trader?

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?

Count the number of triangles in the below picture?

Can you arrange four 9's and use at most 2 math symbols, to make the total 100?

There are are five things wrong with this sentence; only geniuses will be able to to spot all of the mitstakes

If you had a pizza with crust thickness 'a' and radius 'z', what's the volume of the pizza?