ExpertMedium2 marksMultiple Choice
ACCA · Question 10 · Data Analysis and Statistical Techniques
A public utility company monitors the daily electricity consumption of a city. The consumption follows a normal distribution with a mean of 500 MW and a standard deviation of 20 MW.
Approximately what percentage of days will have a consumption between 460 MW and 540 MW?
A public utility company monitors the daily electricity consumption of a city. The consumption follows a normal distribution with a mean of 500 MW and a standard deviation of 20 MW.
Approximately what percentage of days will have a consumption between 460 MW and 540 MW?
Answer options:
A.
68%
B.
95%
C.
99.7%
D.
50%
How to approach this question
Determine how many standard deviations away from the mean the values 460 and 540 are. Apply the empirical rule (68-95-99.7).
Full Answer
B.95%✓ Correct
The range 460 MW to 540 MW represents the mean +/- 40 MW. Since the standard deviation is 20 MW, this is exactly +/- 2 standard deviations. According to the empirical rule of normal distribution, approximately 95% of data falls within 2 standard deviations of the mean.
Common mistakes
Confusing the empirical rule percentages (e.g., selecting 68% which is 1 SD).
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