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:
-y= -4x -4
y= 4x +4
slope is 4
Step-by-step explanation:
N/8 = 25/40
40n = 25 * 8
40n = 200
n = 200/40
n = 5
n/20 = 85/100
100n = 85 * 20
100n = 1700
n = 1700/100
n = 17
2/3 = 16/n
2n = 16 * 3
2n = 48
n = 48/2
n = 24
5/6 = 25/n
5n = 25 * 6
5n = 150
n = 150/5
n = 30