Question

The mean marks obtained by $300$ students in Mathematics are $45$. The mean of top $100$ students was $70$ and the mean of last $100$ was known to be $20$. The mean of remaining $100$ students is

• A. $40$
• B. $50$
• C. $45$
• D. $43$

Answer 1

The correct option is C $45$

Mean marks obtained by $300$ students are $45$

Total marks $=300\times 45$

Top $100$ students mean is $70$

and last $100$ student mean is $20$

Let remaining $100$ student mean $=x$

So $70\times 100+20\times 100+100\times x=300\times 45$

or, $(70+20+x)100=300\times 45$

$90+x=135$

$x=45$