Answer:
A. 27
Step-by-step explanation:
There are 40 students and 90% of them take exams
(40 students) * (0.9) = 36 students took exams
Of those 36 students, 75% (or 3/4) of them passed. Assuming passing exams means graduating:
(36 students) * (0.75 ) = 27 students graduated
Step-by-step explanation:
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To compute the mean, you simply have to sum all the elments in the data set and the divide the sum by the number of elements:

To compute the variance, we first need to compute the distance of each element from the mean. To do so, we build a "parallel" dataset, given by the difference of every value and the mean:


Now we need those difference squared:

The variance is the mean of this new vector, so

Finally, the standard deviation is simply the square root of the variance, so you have

Answer:A
The mean is the average of all numbers, in this example it's to national averages which will have many numbers.