In this task, you need to answer the given multiple-choice question on the general math. Classify your answers into 'a', 'b', 'c', 'd', and 'e'.

Problem: a = 4 ^ 15 - 625 ^ 3 and a / x is an integer , where x is a positive integer greater than 1 , such that it does not have a factor p such that 1 < p < x , then how many different values for x are possible ? 
Options: a ) none , b ) one , c ) two , d ) three , e ) four
c

Problem: for the positive integers x , x + 2 , x + 4 , x + 7 , and x + 17 , the mean is how much greater than the median ? 
Options: a ) 0 , b ) 1 , c ) 2 , d ) 4 , e ) 7
c

Problem: what will be the vulgar fraction of 0.8 
Options: a ) 3 / 5 , b ) 4 / 5 , c ) 3 / 2 , d ) 3 / 7 , e ) 3 / 8

b