Answer:
Fraction in simplest form as 

Explanation:
Given as, 
Fraction of students got A in first period class = 

Fraction of students got A in second period class = 

Now, 
Fraction of more student got A in first period class to second period class = 
 -
 - 

or, 

Or, 
 ,
,
Again covert this fraction in simplest form
simplest form : A fraction is in simplest form, when numerator and denominator can not be any smaller, but still being whole number.
So, this fraction in simplest form as 
 Answer
 Answer