At the airport, ten people are waiting on standby. Two seats become available, one first class and one coach. How many ways are there to fill the two seats?

The two seats are different, so assigning one person to first class and another to coach is an ordered choice. There are 10 choices for first class, then 9 remaining choices for coach: 10 × 9 = 90. Thus, the answer is D, 90 ways.

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