Question

The physical plant at the main campus of a large state university receives daily requests to replace fluorescent light bulbs. The distribution of the number of daily requests is bell-shaped and has a mean of 47 and a standard deviation of 7. Using the empirical rule (as presented in the book), what is the approximate percentage of lightbulb replacement requests numbering between 47 and 68

Answer 1

The approximate percentage of lightbulb replacement requests numbering between 47 and 68 is 49.85%.

Explanation:

The Empirical Rule states that, for a normally distributed random variable:

Approximately 68% of the measures are within 1 standard deviation of the mean.

Approximately 95% of the measures are within 2 standard deviations of the mean.

Approximately 99.7% of the measures are within 3 standard deviations of the mean.

In this problem, we have that:

Mean of 47

Standard deviation of 7

What is the approximate percentage of lightbulb replacement requests numbering between 47 and 68?

The normal distribution is symmetric, which means that 50% of the measures are below the mean and 50% of the above.

Between 47 and 68:

68 = 47 + 7*3

So 68 is three standard deviations of the mean.

Of the 50% above the mean, approximately 99.7% are between the mean of 47 and 3 standard deviations above the mean, which is 68. So

0.5*0.997 = 0.4985

0.4985*100 = 49.85%

The approximate percentage of lightbulb replacement requests numbering between 47 and 68 is 49.85%.