In a class of 100 students there are 70 boys whose average marks in a subject are 75 . If the averag

Question

In a class of 100 students there are 70 boys whose average marks in a subject are 75 . If the average marks of the complete class is 72 , then what is the average marks of the girls?\

Professor PC Thomas Classes · Answer

(b) : We have,\ $\bar{x}=\frac{\left(x_{1}+x_{2}+\ldots+x_{100}ight)}{100}=72$\ $	herefore x_{1}+\ldots+x_{100}=7200$\ Again $\frac{x_{1}+x_{2}+\ldots+x_{70}}{70}=75$\ $\Rightarrow \quad x_{1}+\ldots+x_{70}=75 	imes 70$\ $	herefore \quad$ Average marks of 30 girls $$ =\frac{7200-5250}{30}=65 $$