Suppose that a customer service center claims that the telephone calls it receives last 114 seconds on average, with a standard deviation of 9
seconds. If you took a sample of 324 telephone calls, which of the following
mean times would be within the 95% confidence interval?
A. 115.5 seconds
B. 114.5 seconds
C. 116.5 seconds
D. 117.5 seconds

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step-by-step explanation:

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step-by-step explanation:

hello from mrbilldoesmath!

answer:

(7 x + 6 y) (49 x^2 - 42 x y + 36 y^2)

discussion:

the trick is to recognize that 343 = 7^3 and 216 = 6^3 and, in general,

a^3 + b^3 =   (a + b) (a^2 - a b + b^2).

in our case

343x^3+216y^3   =   (7x)^3 + (6y)^3

so take a = 7x and b = 6y in the above equation to get the answer.

you,

mrb