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Answer:
The 95% confidence interval for the mean amount of the increase is ($541.6, $588.4). This means that we are 95% sure that the mean amount of increase of all customers who charge at least $3,000 in a year is between these two values.
Step-by-step explanation:
We have that to find our level, that is the subtraction of 1 by the confidence interval divided by 2. So:
Now, we have to find z in the Z-table as such z has a p-value of .
That is z with a pvalue of , so Z = 1.96.
Now, find the margin of error M as such
In which is the standard deviation of the population and n is the size of the sample.
The lower end of the interval is the sample mean subtracted by M. So it is 565 - 23.4 = $541.6
The upper end of the interval is the sample mean added to M. So it is 565 + 23.4 = $588.4
The 95% confidence interval for the mean amount of the increase is ($541.6, $588.4). This means that we are 95% sure that the mean amount of increase of all customers who charge at least $3,000 in a year is between these two values.
Answer: They will charge same amount for 360 minutes of calls.
Step-by-step explanation:
A phone company offers two monthly plans plan A cost $9 Plus And additional 0.12 $ for each minute of calls. Plan B cost $27 plus an additional $0.07 for each minute of calls
For what amount of calling do the two plans cost the same?
Let the each minute of calls be 'x'.
So, for plan A would be
plan A cost $9 Plus And additional 0.12 $ for each minute of calls is expressed as
Plan B cost $27 plus an additional $0.07 for each minute of calls is expressed as
According to question, it becomes,
Hence, they will charge same amount for 360 minutes of calls.