Reaction times are normal with mean 72 ms and standard deviation 9 ms. Between which two times do the middle 68% roughly lie?

54 ms and 90 msCorrect answerYour answer45 ms and 99 msCorrect answerYour answer68 ms and 76 msCorrect answerYour answer63 ms and 81 msCorrect answerYour answer

Show the answer and explanation

CorrectNot quiteAnswer D

Correct answer: D

About 68% lie within one standard deviation of the mean.
$72 - 9 = 63$ and $72 + 9 = 81$ .

Worth noting

54 to 90 ms is two standard deviations each way, about 95%.

Concept: The middle 68%
Typical timeTypical: 60 s
Your timeYours: —

The rule this testsUsing the normal distribution

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Reaction times are normal with mean 72 ms and standard deviation 9 ms. Between which two times do the middle 68% roughly lie?

Explanation