Successful 83167

Eighth-grade test results:
8D =?
8B = 47
8A = 44
8E = 37
8C = 28
Class 8A achieved exactly the average result. How many points did the winning class 8D get?
By what % is class 8B more successful than class 8C?

Correct answer:

D =  64
p =  67.8571 %

Step-by-step explanation:

$$\begin{gathered} B=47 \\ A=44 \\ E=37 \\ C=28 \\ \mu =A=44 \\ n=5 \\ \mu =\frac{A+B+C+D+E}{n} \\ D=n\cdot \mu -A-B-C-E=5\cdot 44-44-47-28-37=64 \end{gathered}$$

$p=100\cdot \frac{B-C}{C}=100\cdot \frac{47-28}{28}=67.8571\%$

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