Question

the average marks of 39 students of a class is 50. The marks obtained by 40th students are 39 more than the average marks of all the 40 students. Find the mean marks of all the 40 students

Answer 1

mean=no.of observation /sum of all observation

Answer 2

Answer:

51

Step-by-step explanation:

We are given  that average of marks of 39 students is 50

$Average =\frac{\text{ sum of marks of 39 students}}{39}$

$50 =\frac{\text{ sum of marks of 39 students}}{39}$

$50 \times 39 =\text{ sum of marks of 39 students}$

$1950 =\text{ sum of marks of 39 students}$

So sum of the marks of 39 students is 1950

Let the marks scored by 40th student be x

Average of 40 students marks = $\frac{\text{ sum of marks of 39 students+x}}{40}$

$Average = \frac{1950+x}{40}$

Now we are given that The marks obtained by 40th students are 39 more than the average marks of all the 40 students.

So, $x =39+ \frac{1950+x}{40}$

$x-39=\frac{1950+x}{40}$

$x=90$

So marks scored by 40th student is 90 marks

Now Average of 40 students marks = $\frac{\text{ sum of marks of 39 students+x}}{40}$

Average of 40 students marks = $\frac{1950+90}}{40}$

Average of 40 students marks = $51$

Hence he mean marks of all the 40 students is 51