OFFICIAL EXPLANATION
Let X and Y, respectively, denote the list of the lengths of the logs in shipments X and Y before the transfer (to shipment X) of the two longest logs in shipment Y. Also, let X* and Y*, respectively, denote the list of the lengths of the logs in shipments X and Y after the transfer (to shipment X) of the two longest logs in shipment Y. It is given that the median of list X is 84 and the median of list Y is 85. Determine the median of list X*.
(1) Given that the lengths of the two logs transferred were 91 and 92, it is not possible to determine the median of list X*. For example, suppose list X consisted of 13 occurrences of 84 while list Y consisted of 19 occurrences of 85, 1 occurrence of 91, and 1 occurrence of 92. Then the median of list X is 84, the median of list Y is 85, and the median of list X* is 84 (note that 84 is the 8th number when the 15 numbers in list X* are listed from least to greatest). On the other hand, suppose list X consisted of 7 occurrences of 84 and 6 occurrences of 85, while list Y consisted of 19 occurrences of 85, 1 occurrence of 91, and 1 occurrence of 92. Then the median of list X is 84, the median of list Y is 85, and the median of list X* is 85 (note that 85 is the 8th number when the 15 numbers in list X* are listed from least to greatest); NOT sufficient.
(2) Given that the greatest number in list X is 90, it is not possible to determine the median of list X*. For example, suppose list X consisted of 12 occurrences of 84 and 1 occurrence of 90, while list Y consisted of 19 occurrences of 85, 1 occurrence of 91, and 1 occurrence of 92. Then the median of list X is 84, the median of list Y is 85, and the median of list X* is 84 (note that 84 is the 8th number when the 15 numbers in list X* are listed from least to greatest). On the other hand, suppose list X consisted of 7 occurrences of 84, 5 occurrences of 85, and 1 occurrence of 90, while list Y consisted of 19 occurrences of 85, 1 occurrence of 91, and 1 occurrence of 92. Then the median of list X is 84, the median of list Y is 85, and the median of list X* is 85 (note that 85 is the 8th number when the 15 numbers in list X* are listed from least to greatest); NOT sufficient.
Given (1) and (2) together, the examples given in (2) above show that the median of list X* cannot be determined.
The correct answer is E; both statements together are still not sufficient.