Step-by-step explanation:
Monthly bill - Flat rate = $38.44 - $3.99 = $34.45.
Minutes used = $34.45 / $0.05 = 689.
Answer:
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Step-by-step explanation:
7x-4x=3+3
3x=6
x=2
The 99% confidence interval for the true mean is given by:

where:

is the sample mean = 69.7

is the standard deviation = 2.8

is the test statistics = 2.58 for for 99% confidentce interval.
n is the sample size = 772.
Therefore, the 99% confidence interval is: