What is the coolest letter in the alphabet?

What is the largest number you can write with just 3 digits?

Which tank will fill first?

There is a place where if I stand up straight, I will still be considered sideways.

After teaching his class all about Roman numerals (X = 10, IX=9 and so on) the teacher asked his class to draw a single continuous line and turn IX into 6. The teacher's only stipulation was that the pen could not be lifted from the paper until the line was complete.

What is in seasons, seconds, centuries and minutes but not in decades, years or days?

Can you find the dog hidden in a group of pandas?

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.

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

As easy as you can get into me, it is as hard to get out of me.

Do you know what I am?