Which of the following is closest to the proportion of orders that are processed in less than 240 seconds?

At a small coffee shop, the distribution of the number of seconds it takes for a cashier to process an order is approximately normal with mean 276 seconds and standard deviation 38 seconds. Which of the following is closest to the proportion of orders that are processed in less than 240 seconds?

A. 0.17

B. 0.25

C. 0.36

D. 0.83

E. 0.95

1 Answer

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  • 1 month ago
    Favourite answer

    P(t < 240) => P(z < (240 - 276)/38)

    i.e. P(z < -0.95)

    or P(z > 0.95)

    Hence, 1 - P(z < 0.95)

    From normal tables we have:

    1 - 0.8289 => 0.1711

    so, 0.17 or 17% seems the best estimate

    :)>

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