Question 69

The average score of 40 students in a class test is 45. Later on, it was found that at two places 25 was read as 35 and at one place 38 wasread as 32, What is the actual average score of the class?

The reported average of the class is $$45$$ for $$40$$ students.

Therefore, the reported total score is
$$\text{Reported total}=45 \times 40 = 1800$$

Now compare each wrong entry with the correct value.

Case 1: Two scores were actually $$25$$ but were recorded as $$35$$.
For each such case, the reported value exceeds the true value by $$35-25 = 10$$.
Hence the total excess due to these two cases is $$2 \times 10 = 20$$.

Case 2: One score was actually $$38$$ but was recorded as $$32$$.
Here the reported value is short by $$38-32 = 6$$.

The net error in the reported total is therefore
$$\text{Net error}=+20-6 = +14$$

Because the reported total is $$14$$ more than the true total, the actual total must be
$$\text{Actual total}=1800-14 = 1786$$

The actual average score of the class is then
$$\text{Actual average}= \frac{1786}{40}=44.65$$

Hence, the correct average score is $$44.65$$.
Option D which is: 44.65

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