The area is the sum of 'n' rectangle areas.
The width of the rectangle is size of interval, (domain size)/n
The height of each rectangle is f(interval) as interval moves along domain.
For this example, domain size = 3-1 = 2
size of interval = 2/n
height varies from f(1) to f(3), increasing by 2/n each time.
f(1+(2/n)i)
Putting this together, the area is the sum of:

Since you are given the function f(x). Sub input into f(x) to get area in terms of n and i.

Finally, the summation is:
Answer:
a. The arm spans for Class A have more variability than the arm spans for Class B.
Step-by-step explanation:
The stemplot for the Arm span is given for Class A and Class B. The variability of Class A are higher than variability of Class B. The arm spans of Class A have values greater than Class B. The mean of Class A is greater than Class B.
So according to the question statements
6% of the $40k and 7$ of the second $40k and 9% ammount of the $80k
the answer would be
40000 * 0.06
+ 40000 * 0.07
+ 25000 * 0.09
= 270250