bmwhype2 wrote:

A plane takes off from a hill at 750 meters above sea level and lands some time later in a town located at 50 meters below sea level. During the first part of its flight, the plane gained height at a rate of 50 meters per minute but then it started to descend at a rate of 20 meters per minute. The duration of the first part of the flight was what percent of the total flight time?

1. The duration of the descent is known.

2. The total flight time is known.

Source: GMAT Club Tests - hardest GMAT questions

IMO the question is rongly worded; If quations ask for actual numbers then we have to answer wether we can calculate the number based on the statements . However, the statement povided does not provide enough information to calulate the exact percentage, therefore both statements are insufficient.

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