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Problem-Solving and Data Analysis / One-variable data: Distributions and measures of center and spread Difficulty: Easy

The figure presents a bar graph titled “Results of Five Quality Control Trials.” The horizontal axis is labeled “Trial,” and the following five letters are indicated along the axis: A, B, C, D, and E. Each letter has a vertical bar. The vertical axis is labeled “Number of defective light bulbs,” and the numbers 0 through 8, in increments of 1, are indicated. The data represented by each of the 5 bars are as follows. Trial A, 4 light bulbs. Trial B, 7 light bulbs. Trial C, 1 light bulb. Trial D, 3 light bulbs. Trial E, 6 light bulbs.

For quality control, a company that manufactures lightbulbs conducted five different trials. In each trial, 500 different lightbulbs were tested. The bar graph above shows the number of defective lightbulbs found in each trial. What is the mean number of defective lightbulbs for the five trials?

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Explanation

Choice B is correct. The numbers of defective lightbulbs found for the five trials are 4, 7, 1, 3, and 6, respectively. The mean is therefore the fraction with numerator 4, plus 7, plus 1, plus 3, plus 6, and denominator 5, equals 4 point 2.

Choice A is incorrect. This is the median number of defective lightbulbs for the five trials. Choice C is incorrect and may result from an arithmetic error. Choice D is incorrect and may result from mistaking the number of trials for the number of defective lightbulbs.