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

O T T F F S S ?

I am white when I am dirty, and black when I am clean. What am I?

When a clock is observed, the hour hand is at a minute mark and the minutes hand is six minutes ahead of it.

When the clock is observed again after some time, the hour hand is precisely on a different minute mark and the minute hand is seven minutes ahead of it.

Can you calculate how much time has elapsed between the two observations?

What you cannot hold but it is yours?

Be active and find the killer in the picture Riddle below.

I’m orange, I wear a green hat and I sound like a parrot. What am I?

You are in a land where thirty men and two women were dressed in classic black and white dresses.
They begin to fight as soon as any of them move.

Where are you?

Below, you will find the mathematical proof that 10 equals 9.99999?. But is that possible or there is something wrong about it? Can you find the error?

x = 9.999999...
10x = 99.999999...
10x - x = 90
9x = 90
x = 10

How many times can you subtract the number 5 from 25?

I shave every day, but my beard stays the same. What am I?