Replace the question mark with the number below given a simple math problem.

A maths symbol is hidden in the below Bar Graph. Can you decipher it?

In an Art Gallary, When the clock hit 11 am, Artist hung the painting number 30. When it struck 4 pm, he hung painting number 240 and when it struck 7:30 pm, he hung painting number 315.

Can you determine, which painting number will he hang when the time is 9:20 pm?

If I put in one canary per cage, I have one bird too many. If I put in two canaries per cage, I have one cage too many. How many cages and canaries do I have?

Detective Rockford was jogging near the beach at 4:30 am.
He hears a sound near the shack "No Michael, Please Do not shoot me".
Next instance he heard the sound of gunfire. Rockford rushes to the shack where he finds women lying dead and a gun in close proximity of three "Doctore Lawyer and a Teacher".

Rockford immediately knew that the Lawyer has committed the crime. How?

What is the word or phrase?

Why do you find that most of the buildings are deprived of the 13th floor?

A shepherd had 18 sheep, out of which, all but ten died.

Can you tell us how many sheep was he left with?

You are given a set of weighing scales and 12 marbles. The scales are of the old balance variety. That is, a small dish hangs from each end of a rod that is balanced in the middle. The device enables you to conclude either that the contents of the dishes weigh the same or that the dish that falls lower has heavier contents than the other. The 12 marbles appear to be identical. 11 of them are identical, and one is of a different weight. Your task is to identify the unusual marble and discard it. You are allowed to use the scales three times if you wish, but no more. Note that the unusual marble may be heavier or lighter than the others. You are asked to both identify it and determine whether it is heavy or light

In the image below, you can see two glasses and two matchsticks.You need to move four matchsticks in such a manner that the crosses come inside the glasses. Note: you cannot move the crossed.