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 are $72$, then what are the average marks of the girls?

• A. $73$
• B. $65$
• C. $68$
• D. $74$

Answer 1

The correct option is B

$65$

Explanation for the correct option:

Finding the average marks of girls:

Given,

The total given number of students in class $=100$

Out of which number of boys,$=70$

Hence, the number of girls in class $=(100–70)$

$=30$

Now, the total marks of $100$ students$=100x72$

$=7200$

Similarly, the marks of $70$ boys$=70x75$

$=5250$

Therefore, the marks of $30$ girls $=7200–5250$

$=1950$.

So, the average marks of $30$ girls $=\frac{1950}{30}$

$=65$.

Hence, the correct option is C.