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10-67.

Eight friends go to the movies. They want to sit together in a row with a student on each aisle. (Assume the row is $8$ seats wide including $2$ aisle seats.)

1. How many ways can they sit in the row?

$8! = 40,320$

2. If Kristen wants to sit in an aisle seat, how many ways can they all sit in the row?

If one person's position is already decided, how many ways can the rest be arranged?

She can sit in either aisle seat.

3. If Annabeth wants to sit on an aisle seat with Ian next to her, how many ways can the eight students sit?

If two people's positions are already set, how many ways can the others be arranged?