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Precision and Accuracy

On Thursday, ...

Question

On Thursday, $20$ of the $25$ students in a chemistry class took a test and their average (arithmetic mean) was $80$ . On Friday, the other $5$ students took the test and their average (arithmetic mean) was $90.$ What was the average for the entire class?

A

82

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B

83

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C

84

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D

85

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Solution

The correct option is B $82$
Average $= \frac{20 (80) + 5 (90)}{25} = \frac{1600 + 450}{25} = \frac{2050}{25} = 82$

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