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10-98.

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 on the far left 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?

3. If Kristen wants either aisle seat, how many ways can the eight students sit?

Since Kristen can sit in either aisle seat, how many more ways could everyone be arranged?

$1 · 7!$ for sitting on the left $+ 1 · 7!$ for sitting on the right aisle.