My calculator gave me 22 but download Calculate84 and see if you get the same answers
The best group to take a sample from would be the eighth graders because they are the ones who will be participating in the dance, so they should have the most input.
ANSWER
D) 10
EXPLANATION
We want to solve the radical equation,

Square both sides,

Expand brackets on right hand side,

Rewrite in general quadratic equation form,

Factor to obtain,

Apply the zero product principle to get,

We put n=2 into the equation to get,


This statement is false, hence 2 is an extraneous solution
We put n=10, to get



This is true, hence the only solution is