Delivery times are normal with mean 30 minutes and standard deviation 4 minutes. Between which two times do about 95% of deliveries fall?

22 and 38 minutesCorrect answerYour answer26 and 34 minutesCorrect answerYour answer18 and 42 minutesCorrect answerYour answer28 and 32 minutesCorrect answerYour answer

Show the answer and explanation

CorrectNot quiteAnswer A

Correct answer: A

About 95% lie within two standard deviations of the mean.
$30 - 8 = 22$ and $30 + 8 = 38$ minutes.

Worth noting

26 to 34 minutes is one standard deviation each way, about 68%.

Concept: The middle 95%
Typical timeTypical: 60 s
Your timeYours: —

The rule this testsUsing the normal distribution

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Delivery times are normal with mean 30 minutes and standard deviation 4 minutes. Between which two times do about 95% of deliveries fall?

Explanation