Total

In one class, 1 student collected an average of 20 kg of paper, in the second class 30 kg, and in the third class 40 kg. How many kilograms of paper did 1 student collect on average for all three classes together, when the second class had the same number of students as in the first class, but the third class had half the number of students compared to the first and second classes?

Correct answer:

x =  28 kg

Step-by-step explanation:

$$\begin{gathered} x=(20\cdot n+30\cdot n+40\cdot n/2)/(n+n+n/2) \\ x=(20+30+40\cdot 1/2)/(1+1+1/2)=28\text{kg} \end{gathered}$$

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