What percentage of the app's deliveries take…

What percentage of the app's deliveries take between 36 and 56 minutes?

Question 60

MediumOriginal question

A food-delivery app's delivery times are normally distributed with mean 40 minutes and standard deviation 8 minutes. (Take $P(0 < Z < 0.5) = 0.1915$ , $P(0 < Z < 0.75) = 0.2734$ , $P(0 < Z < 1.645) = 0.45$ and $P(0 < Z < 2) = 0.4772$ .)

What percentage of the app's deliveries take between 36 and 56 minutes?

28.57%Correct answerYour answer47.72%Correct answerYour answer65.87%Correct answerYour answer66.87%Correct answerYour answer

Show the answer and explanation

CorrectNot quiteAnswer D

Correct answer: D

36 minutes is $z = -0.5$ and 56 minutes is $z = 2$ .
$0.1915 + 0.4772 = 0.6687$ , so 66.87%.

Worth noting

28.57% subtracts the two areas, though the values lie on opposite sides of the mean.

Concept: A share across the mean
Typical timeTypical: 120 s
Your timeYours: —

The rule this testsUsing the normal distribution

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Ten questions from Normal Distribution, at your own pace.

Practise this chapter →

Ten questions from Normal Distribution, at your own pace.

What percentage of the app's deliveries take between 36 and 56 minutes?

Question 60

Explanation