I had this Q in mock exam ( %probability)

The distance between 80 and the mean of 58 is 22, which is 22/10 or 2.2 standard deviations (and is the z-score). From the normal distribution tables, the probability of being between 58 and 80 is therefore 0.4861. Because of symmetry, the probability of being above the mean of 58 is 0.5. Therefore the probability of being more than 80 is 0.5 - 0.4861 = 0.0139 (or 1.39%) Using the normal distribution is all dealt with in my free notes and the free lectures that work through and explain the notes.

Hi! I didn't understand anything and gone through lecture notes as well...

But did you watch the lectures? It is completely pointless to use our lecture notes without watching the free lectures that work through them.

I don't understand from where did 0.5 came from? I just had another mock test with again two questions which are almost identical to this one just different numbers... I really have no idea :/

The normal distribution is symmetrical about the mean. There is therefore a 0.5 (50%) chance of being either above or below the mean. I ask again - have you actually watched my free lectures where all this is explained in detail? You cannot expect me to type out all of my lectures here :-)