Why is a river so rich ?

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

In a competitive exam, each correct answer could win you 10 points and each wrong answer could lose you 5 points. You sat in the exam and answered all the 20 questions, which were given in the exam.
When you checked the result, you scored 125 marks on the test.

Can you calculate how many answers given by you were wrong?

There are 2 cops parked along a one-way street looking for traffic violations. They spot a taxi driver going in the wrong direction, yet they do nothing.

Why?

Find the next number in the sequence

5 12 24 36 ?

What is next number in the pattern below:

131 517 192 123 ?

What does the below rebus riddle means?

I am quite hot but become too cold if you remove the first two letters. What am I?

What is the word or phrase?

There are three light switches outside a room. One of the switches is connected to a light bulb inside the room.
Each of the three switches can be either 'ON' or 'OFF'.

You are allowed to set each switch the way you want it and then enter the room(note: you can enter the room only once)

Your task is to then determine which switch controls the bulb?