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  • 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

 

Answers (1)

best_answer

As we learnt in

ARITHMETIC Mean -

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

\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

Posted by

divya.saini

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