What is always in front of you but can’t be seen?

using four eights (8) and a one (1) and one mathematical symbol , create the number 100

Place the numbers from 1 to 9 in the circles in a manner that each side of the triangle sums up to 17.

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?

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

? : 3839 :: 11 : 1209

A lion and its tamer are standing inside a cage that measures 1 unit in radius. Both of them can effortlessly run at the speed of 1 unit maximum.

1) Suppose the lion is hungry, will he be able to eat up the tamer?
2) If yes, how long can the tamer survive?

After undergoing a successful eye operation, A blind girl has just boarded a train to her home. The doctor asked her to open the bandages after 3 hours. On her train journey, she opened the bandages and within a fraction of the time she commits suicide by jumping off the train.

Though her operation was successful, Why did she commit suicide?

Look at the below sequence of letters and tell us what the next letter should be:

O T T F F S S ?

81 x 9 = 801. What must you do to make the this equation true?

What number do you get when you multiply all of the numbers on a telephone's number pad?