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Problem-Solving and Data Analysis / Percentages Difficulty: Medium

A customer’s monthly water bill was $75.74. Due to a rate increase, her monthly bill is now $79.86. To the nearest tenth of a percent, by what percent did the amount of the customer’s water bill increase?

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Explanation

Choice D is correct. To find the percent increase of the customer’s water bill, the absolute increase of the bill, in dollars, is divided by the original amount of the bill, and the result is multiplied by 100%, as follows: $the fraction with numerator 79 point 8 6 minus 75 point 7 4, and denominator 75 point 7 4, is approximately equal to, 0 point 0 5 4;$ ; $0 point 0 5 4 times 100 percent, equals 5 point 4 percent$ .

Choice A is incorrect. This choice is the difference $79 point 8 6, minus 75 point 7 4$ rounded to the nearest tenth, which is the (absolute) increase of the bill’s amount, not its percent increase. Choice B is incorrect and may be the result of some calculation errors. Choice C is incorrect and is the result of dividing the difference between the two bill amounts by the new bill amount instead of the original bill amount.