The average marks of a class of 30 students is 40 and that of another class of 50 students is 90. Find the average marks of all the students?	Choose the correct choice from the following answers.
A) 71.25
B) 52.9
C) 52.1
D) 52.3
E) 42.5
Sum of the marks for the class of 30 students = 30 * 40= 
<gadget id="calculator">30 * 40</gadget>
<output>1_200</output>
1200   Sum of the marks for the class of 50 students= 50 * 90= 
<gadget id="calculator">50 * 90</gadget>
<output>4_500</output>
4500   Sum of the marks for the class of 80 students=   1200 + 4500= 
<gadget id="calculator">1200 + 4500</gadget>
<output>5_700</output>
5700   71.25verage marks of all the students= 5700/80= 
<gadget id="calculator">5700/80</gadget>
<output>285/4 = around 71.25</output>
71.25   71.25nswer:71.25
<result>A</result>
The average marks of a class of 30 students is 40 and that of another class of 50 students is 90. Find the average marks of all the students?