Question 1094705
%age of questionnaires will not be returned = 30%
%age of questionnaires returned = 70%
no of questionnairs returned = 750 
also we know that 
 (no. of question returned)
___________________________   * 100  = 70% (given)
 total number of question sent 
 
therefore total number of question sent = (750*100)/70 
                                        =  1072 (atleast)