Question 1

There are 5 doors to a lecture room. What is the number of ways that a student enters the room and leaves it by different doors?

1. 10
2. 9
3. 20
4. 625
5. 1024

The correct Answer is 20 ways and the correct Choice is (C).

There are 5 doors to the lecture room.
The student would have entered the lecture room using one of the 5 doors in 5 ways.

Now, if she has to leave the lecture room by a different door, then she has to take one of the remaining 4 doors.
She can select one of the four doors to exit the lecture room in 4 ways.

Therefore, the total number of ways a student enters the lecture room and leaves it by different doors = 5 * 4 = 20 ways.

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