What is both possible and impossible at the same time?

A brand new Mobile Phone was on sale at 20% as a promotional offer. By what per cent must the Mobile price be increased to sell it at the original price again?

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

which number am I?

You want to boil a two-minute egg. If you only have a three-minute timer (hourglass), a four-minute timer and a five-minute timer, how can you boil the egg for only two minutes?

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.

Can you place six X (crosses) in below board without making three in a row in any way ?

I am a seven-letter word but if you remove four of my letters I will have one left. What word am I?

It walks on 4 when its young, walks on 2 when it's older, and walks on 3 when its very old?

what does the below rebus means?

Rob is taller than Edwin, and Jurgen is shorter than Rob.
Of only one of the following statements, we now certainly know it is correct:

A.Edwin is taller than Jurgen
B.Jurgen is taller than Edwin
C.It cannot be determined if Jurgen or Edwin is the tallest.