Answer:
99.7% of customers have to wait between 8 minutes to 30 minutes for their food.
Step-by-step explanation:
We are given the following in the question:
Mean, μ = 18 minutes
Standard Deviation, σ = 4 minutes
We are given that the distribution of amount of time is a bell shaped distribution that is a normal distribution.
Empirical Formula:
- Almost all the data lies within three standard deviation from the mean for a normally distributed data.
- About 68% of data lies within one standard deviation from the mean.
- About 95% of data lies within two standard deviations of the mean.
- About 99.7% of data lies within three standard deviation of the mean.
Thus, 99.7% of the customers have to wait:

Thus, 99.7% of customers have to wait between 8 minutes to 30 minutes for their food.
Answer:
C. 90
Step-by-step explanation:
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Answer:
65.45
Step-by-step explanation:
Zscore = (x - mean) / standard deviation
x = score
Percentage below C :
D = 18% ; F = 12%
Sum = 30%
Obtain the Zscore for the proportion below D
P(Z < 0.30) = -0.524
Hence, Zscore = -0.524
Put Zscore = -0.524 in the equation :
-0.524 = (x - 72) / 12.5
-0.524 * 12.5 = x - 72
-6.55 = x - 72
-6.55 + 72 = x
x = 65.45
To receive a grade of C or better, score must be atleast 65.45