Task: Question Answering
Input (English): Problem: 3 students appear at an examination of mathematics . the probability of their success are 1 / 2 , 1 / 4 , 1 / 5 respectively . find the probability of success of at least two . 
Options: a ) 1 / 60 , b ) 2 / 50 , c ) 9 / 40 , d ) 3 / 40 , e ) 4 / 50
Output (English): c