Question

Write the sigma notation mean formula for the second semester beginning in February and determine that semester average rounded to the nearest dollar.

Answer 1

We want to write the formula to evaluate the average for the second semester, which means we will use Feb, Mar, Apr, and May to evaluate it, they are

$x_6,x_7,x_8,x_9$

Writing the formula:

$\mu=\frac{x_6+x_7+x_8+x_9}{4}=\frac{\sum_{n\mathop{=}6}^9x_n}{4}$

Or

$\mu=\frac{1}{4}\sum_{n\mathop{=}6}^9x_n$

Which is

$\mu=\frac{1}{4}\sum_{n\mathop{=}6}^9x_n=\frac{80+78+78+67}{4}=\frac{303}{4}=\ 75.75$

Rounding it to the nearest dollar:

$\mu=\ 76$

The average cable bill is $76