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
(x+12)(x-3) Try this answer hopefully it is correct.
Answer:
11
Step-by-step explanation:
Opposite sides are congruent at parallelograms. So x+16 must be equal to 2x+5. Solve the equation;
2x+5 = x+16
x = 11 .
Answer:
19 square millimeter
Step-by-step explanation: