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There are two sections A and B of a class, consisting of 36 and 44 students’ respectively.

If the average weight of section A is 40kg and that of section B is 35kg, find the average weight of the whole class.


30.00 kg


35.00 kg


37.25 kg


42.50 kg

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Option(C) is correct

Total weight of $(36+44=80)$ Students $= (36 \times 40+44 \times 35)$ kg = 2980 kg

Therefore average weight of the whole class $= \left(\dfrac{2980}{80}\right)$ kg

Therefore average weight = 37.25kg

Edit: For an alternative solution, check comment by Sravan Reddy.

(5) Comment(s)

Umang Uniya

it is very easy in all cases i.e



If we add both the averages and divide it by 2 then also we get the same answer.



You got lucky in this case. But this will not work in every case as this is a wrong technique.

You need to consider weighted averages for the correct solution.

Sravan Reddy

Other way of solving (finally boils down to simplifying the calculation):

=> Assume that the 40 kg batch of 36 are also 35kg. So, average is straight forward 35. Now extra weight is the additional 5 kg from those 36 students - 180kg. So divide that 180 among $44+36 = 80$ students

=> So answer is $35 + \dfrac{180}{80} = 37.25$

P.S. It is similar to simplifying the equation of $\dfrac{(36*40)+(44*35)}{80}$ as $\dfrac{(36*5)+(36*35)+(44*35)}{80} = \dfrac{36*5}{80}+35$.

But this way of thinking gets us the answer in less than 20 sec by mind calculation :)

Manish Singh

We divided it by 80. because 2980 is the total weight of whole class (section $A$ and $B$).

We need to calculate the average of the whole class. and the sum of the students of section $A$ and $B$ is $34+ 46=80.$