Question

@ The average mark of a class is 35. There are 5 girls and their average is 15. The remaining boys have 39 as their average mark. The no of students in the class is

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Answer 1

Answer:

Step-by-step explanation:

The average marks of 5 girls is 15. Therefore the total girls marks is 15*5=75

Now the average marks for boys is 39. Therefore let the boys number be (X-5). Hence total boys marks are 39X-39*5

Now total marks of class is X*35. As the average marks of class is 35.

Hence by equating above 3 equations we get

75+39X-195=35X

4X=120

X=30

Therefore number of students here is X which is 30

Answer 2

Answer:

The number of students in the class is 30

Step-by-step explanation:

Formula used:

$Combined\:average,\bar{x}=\frac{n_1\:\bar{x_1}+n_2\:\bar{x_2}}{n_1+n_2}$

Given:

Combined average, $\bar{x}= 35$

Number of girls, $n_1= 5$

Average of girls marks, $\bar{x_1}=15$

Number of boys, $n_2= x(say)$

Average of boys marks, $\bar{x_2}=39$

Now,

$Combined\:average,\bar{x}=\frac{n_1\:\bar{x_1}+n_2\:\bar{x_2}}{n_1+n_2}$

$35=\frac{(5)(15)+(x)(39)}{5+x}$

$35=\frac{75+39x}{5+x}$

$35(5+x)=75+39x$

$175+35x=75+39x$

rearranging terms we get

$175-75=39x-35x$

$100=4x$

$x=\frac{100}{4}$

$x=25$

Therefore, number of students in the class = 5+x = 5+25 = 30