Official Solution:A survey was sent to 80 customers, 7 of whom responded. Then the survey was redesigned and sent to another 63 customers, 9 of whom responded. By approximately what percent did the response rate increase from the original survey to the redesigned survey? A. 2%
B. 5%
C. 14%
D. 28%
E. 63%
To calculate the percent increase of any value, we use this formula: \(\frac{\text{New} - \text{Old}}{\text{Old}}\). In other words, we subtract the original value \(\text{Old}\) from the increased value \(\text{New}\), then divide the result by the original value \(\text{Old}\). Even though the values themselves may be written using percents, we must be sure to divide by the original value.
In this problem, the original response rate is \(\frac{7}{80}\). The new response rate is \(\frac{9}{63}\), or \(\frac{1}{7}\). The difference is \(\frac{1}{7} - \frac{7}{80}\). We convert to common denominators: \(\frac{80}{560} - \frac{49}{560} = \frac{31}{560}\). Now, we divide by the original value, \(\frac{7}{80}\). Doing so is the same as multiplying by \(\frac{80}{7}\). This gives us \(\frac{31}{560}*\frac{80}{7} = \frac{31}{49}\). Estimating, we can see that this fraction is slightly more than \(\frac{30}{50}\), which is \(\frac{60}{100}\) or 60%. Thus, the correct answer must be (E): 63%.
Note that the response rates may be written as percents. For instance, the original response rate \(= \frac{7}{80} = 0.0875 = 8.75%\). Likewise, the new response rate \(= \frac{9}{63} = \frac{1}{7} \approx 14.3%\). However, if you write these rates this way, do not simply take the difference! That difference, approximately 5 or 6%, does NOT represent the percent increase in the response rate. You must divide by the original response rate.
Answer: E
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