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Lara is a wildlife researcher. They were analyzing the mean and median lengths of 77 fish their team had observed. The fish all had different lengths between 15cm15\,\text{cm} and 33cm33\,\text{cm}. Lara found out that they were misreading the longest length. It was actually 88cm88\,\text{cm}, not 33cm33\,\text{cm}. How will this length increasing affect the mean and median? Choose 11 answer:\newline(A) Both the mean and median will increase.\newline(B) The mean will increase, and the median will stay the same.\newline(C) The mean will increase, and the median will decrease.\newline(D) The mean will stay the same, and the median will increase.

Full solution

Q. Lara is a wildlife researcher. They were analyzing the mean and median lengths of 77 fish their team had observed. The fish all had different lengths between 15cm15\,\text{cm} and 33cm33\,\text{cm}. Lara found out that they were misreading the longest length. It was actually 88cm88\,\text{cm}, not 33cm33\,\text{cm}. How will this length increasing affect the mean and median? Choose 11 answer:\newline(A) Both the mean and median will increase.\newline(B) The mean will increase, and the median will stay the same.\newline(C) The mean will increase, and the median will decrease.\newline(D) The mean will stay the same, and the median will increase.
  1. Mean and Median Properties: Lara is analyzing the lengths of 77 fish. To understand how the change in the longest fish length affects the mean and median, we first need to consider the properties of mean and median. The mean is the average of all values, so if one value increases, the mean will also increase. The median is the middle value when all values are ordered from least to greatest. Since there are 77 fish, the median is the length of the 44th fish. Changing the length of the longest fish (the 77th fish) does not affect the position of the median unless the new length causes a shift in the order, which is not the case here.
  2. Calculating Original Mean: To calculate the original mean, we would add up all the fish lengths and divide by 77. However, we do not have the exact lengths of the first 66 fish, only that they are between 15cm15\,\text{cm} and 33cm33\,\text{cm}. Since the longest fish was originally thought to be 33cm33\,\text{cm}, the mean was calculated with this value. With the new length of 88cm88\,\text{cm}, we will add this to the sum of the other 66 fish lengths and then divide by 77 to find the new mean.
  3. Determining Original Median: The original median is the length of the 4th4^{\text{th}} fish. Since we are told that all fish had different lengths and the longest was 3333cm, the median would be less than or equal to 3333cm. With the longest fish now being 8888cm, the median remains the length of the 4th4^{\text{th}} fish, which is unchanged because the order of the first 66 fish lengths is still the same.
  4. Effect of Longest Fish Length Change: Therefore, the mean will increase because the sum of the lengths is now greater with the 88cm88\,\text{cm} fish included. The median will stay the same because it is determined by the middle value, which is unaffected by the change in the longest fish length.

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