In each of the following questions is followed by information given in three statements. You have to study the questions along with the statements and decide the information given in which of the statement(s) is necessary and sufficient to answer the question.
What is the average weight of the girls in the class ?
I. Average weight of all the 60 students is 42 kg.
II. Average weight of boy is 43 kg.
III. Total weight of all girls together is 1144 kg.
Clearly, each statement alone is not sufficient.
I & II : Let no. of girls = x
No. of boys = 60-x
Total weight of all students = 60*42 = 2520
Total weight of boys = 43*(60-x) = 2580-43x
Total weight of all girls = 2520-(2580-43x) = 43x-60
Average weight of girls = $$\frac{43x-60}{x}$$
Since, x is unknown, we cannot proceed further.
Thus, I & II together are not sufficient.
I,II & III : Total weight of all girls = 43x - 60 = 1144
=> x = 1204/43 => x = 28
Thus, Average weight of all girls = 1144/28 = 40.85
Thus, all statements together are sufficient.
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