In a class there are 21 boys and 29 girls. In an exam the average mark of boys in the class is 40 and the average mark of the girls in the class is 42. What is the average mark of the whole class?

 a) 41.16
 b) 40.5
 c) 41
 d) 41.33

41.16.

Solution
Total mark of 21 boys = (21 x 40) = 840
Total mark of 29 girls = (29 x 42) = 1218
Average mark of 50 students = (840 + 1218)/50 = 41.16