Average marks : then and now. 
The average marks per student in a class of $30$ students were $45$. On rechecking it was found that marks
  had been entered wrongly in two cases. After correction these marks were increased by $24$ and $34$ in the
  two cases. The correct average marks per student are
$(1) 75 ;\ \ (2) 60 ;\ \ (3) 56 ;\ \ (4) 47.$

On the first look this looked very easy but when done I was left guessing I did not understand the question  properly.
The average marks per student in a class of $30$ students were $45$ when the counting was flawed. So total marks in that case was $30\times 45=1350$ . Suppose for student $A$ and $B$ marks had been entered wrongly as $'a'$ and $'b'.$ After rechecking the marks were increased by $24$ and $34$. So , now $A$ has $a+24$ and $B$ has $b+34$. So total marks now is $1350+24+34=1408$.  Then the correct average  is $1408/30 =46.93$  which is not same as any of the options. 
So has there been a mistake  in printing  or my understanding $?$

Your understanding looks correct to me.
I'm guessing that either there was a typo (it's supposed to be $26$ and $34$ or $24$ and $36$) or you're expected to round your answer to the nearest integer for some reason.
