Q

# Need clarity, kindly explain! 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 of the girls?

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 of the girls?

• Option 1)

73

• Option 2)

65

• Option 3)

68

• Option 4)

74

132 Views

As we learnt in

ARITHMETIC Mean -

For the values x1, x2, ....xn of the variant x the arithmetic mean is given by

$\dpi{100} \bar{x}= \frac{x_{1}+x_{2}+x_{3}+\cdots +x_{n}}{n}$

in case of discrete data.

-

$\frac{\sum_{i=1}^{100}x_i}{70} =75 =\frac{S_B}{70}$

Also $\frac{\sum_{i=1}^{100}x_i}{100} =72 =\frac{S_T}{100}$

$S_B=5250, \: S_T=7200$

$S_G= 1950$

Thus mean gives$= \frac{1950}{30}=\:65$

Option 1)

73

Incorrect

Option 2)

65

Correct

Option 3)

68

Incorrect

Option 4)

74

Incorrect

Exams
Articles
Questions