Answer:

--- Variance
Step-by-step explanation:
Given

Solving (a): Calculate the mean.
The given data is a grouped data. So, first we calculate the class midpoint (x)
For 51 - 58.

For 59 - 66

For 67 - 74

For 75 - 82

For 83 - 90

So, the table becomes:

The mean is then calculated as:



-- approximated
Solving (b): The sample variance:
This is calculated as:

So, we have:


-- approximated
Answer:
a n = -3+(n-1)-30
Step-by-step explanation:
-3 - 30 = -33
-33 - 30 = -63
-63 - 30 = -93
The common difference here is -30. d = -30
The explicit formula is a n = a1 + (n-1)d
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