Question

In a mid-size company, the distribution of the number of phone calls answered each day by each of the 12 receptionists is bell-shaped and has a mean of 61 and a standard deviation of 8. Using the Standard Deviation Rule (as presented in the book), what is the approximate percentage of daily phone calls numbering between 53 and 69?

Answer 1

68%

Explanation:

The Standard Deviation Rule = Empirical rule formula states that:

68% of data falls within 1 standard deviation from the mean - that means between μ - σ and μ + σ.

95% of data falls within 2 standard deviations from the mean - between μ – 2σ and μ + 2σ.

99.7% of data falls within 3 standard deviations from the mean - between μ - 3σ and μ + 3σ.

From the question,

Step 1

We have to find the number of Standard deviation from the mean. This is represented as x in the formula

μ = Mean = 61

σ = Standard Deviation = 8

For x = 53

μ - xσ

53 = 61 - 8x

8x = 61 - 53

8x = 8

x = 8/8

x = 1

For x = 69

μ + xσ

69 = 61 + 8x

8x = 69 - 61

8x = 8

x = 8/8

x = 1

This falls within 1 standard deviation of the mean where: 68% of data falls within 1 standard deviation from the mean - that means between μ - σ and μ + σ.

Therefore, according to the Standard Deviation Rule, the approximate percentage of daily phone calls numbering between 53 and 69 is 68%