There are 7 people, and 2 of them are grandma, and grandpa.
7 of them have to sit on a car, which has seats located as following: 2 seats in the front, 3 seats in the middle, 2 seats in the back.
Grandma and grandpa MUST sit in the middle.
How many possible different ways of them sitting?
Thank you.
Okay, so first let's put Grandma and Grandpa in the middle.
You have $3$ ways to seat Grandma, and then you have $2$ ways to seat Grandpa. Then you can choose from $5$ other people to put in the last seat in the middle row.
Then, you have $4$ ways to choose a person in the drivers seat, $3$ ways to choose the person in the front passenger seat, $2$ ways to choose for the left-back seat, and only $1$ remaining way to choose the right back seat.
So, your answer is $3\cdot 2\cdot 5\cdot 4!=720$ ways.