Students of three different classes appeared in common examination. Pass average of 10 students of first class was 70%, pass average of 15 students of second class was 60% and pass average of 25 students of third class was 80% then what will be the pass average of all students of three classes?

Students of three different classes appeared in common examination. Pass average of 10 students of first class was 70%, pass average of 15 students of second class was 60% and pass average of 25 students of third class was 80% then what will be the pass average of all students of three classes? Correct Answer 72%

$$\eqalign{ & {\text{Sum}}\,{\text{of}}\,{\text{pass}}\,{\text{student}}\,{\text{}}\,{\text{first,}}\,{\text{second}}\,{\text{and}}\,{\text{third}}\,{\text{class}}, \cr & = \left( {70\% \,{\text{of}}\,10} \right) + \left( {60\% \,{\text{of}}\,15} \right) + \left( {80\% \,{\text{of}}\,25} \right) \cr & = 7 + 9 + 20 = 36 \cr & {\text{Total}}\,{\text{students}}\,{\text{appeared}}, \cr & = 10 + 15 + 25 = 50 \cr & {\text{Pass}}\,{\text{average}}, \cr & = 36 \times \frac{{100}}{{50}} = 72\% \cr} $$