Average marks of 15 students of class first is 160. Average marks of 10 students of class second is 120. Average marks of 15 students of class third is 180. What will be the average marks of students of all the classes together?
Total marks of 15 students of class first = 15*160 = 2400
Total marks of 10 students of class second = 10*120 = 1200
Total marks of 15 students of class third = 15*180 = 2700
Therefore, Required average $$=\dfrac{2400+1200+2700}{15+10+15} = \dfrac{6300}{40} = 157.5$$
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