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If we start to play a "what, if" game we can assume that #1 reads as "X descends 9 times faster than Y ascends" and the answer would be (D), because #1 is also sufficient
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bono
If we start to play a "what, if" game we can assume that #1 reads as "X descends 9 times faster than Y ascends" and the answer would be (D), because #1 is also sufficient


#1 is NOT sufficient. If Y scales up by a factor of 2, so does X and they APPROACH each other quicker.
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bono
If we start to play a "what, if" game we can assume that #1 reads as "X descends 9 times faster than Y ascends" and the answer would be (D), because #1 is also sufficient


You are mistaken.

With the information "X descends 9 times faster than Y ascends", you cannot know how long it will take them to meet. What if X descends at 9000000 mph and Y ascends at 1000000 mph. Don't you think they will meet a lot quicker than if X descends at 9 mph and Y at 1 mph? I believe you misread the question stem to mean "at what altitude (or relative to one of the plane's altitudes) will they meet. That question can be answered, because the speed does not matter, only the relative speed.

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