There are 2 people near the river and both of them want to get on the other side. The boat can only take one of them. But they got across.
How?

Replace the question mark with the correct number, given the pair of numbers exhibits a similar relationship?

? : 3839 :: 11 : 1209

John was working on a Chemical Mixture whose weight comprise 90% liquid and 10% solid. The total weight of the mixture is 20 pounds. After a while, John noticed that some of the liquid evaporated and now the liquid comprises just 50% of the weight.

What is the weight of the chemical mixture now?

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?

What makes this number unique: 8,549,176,320?

I am a prime number.
The double of myself is equal to the square of me.

which number am I?

Replace the question mark in the picture below.

Count the Triangle in the figure given below:

I am sure no one can have two things for dinner. what are they?

Why is a river so rich ?