#36, For each real number x, let u(x) be the mean of the numbers, 4, 9, 7, 5 and x; and let n(x) be the median of these numbers. For how many values of x is u(x) = n(x)?

Ans: D, Three.

Can anyone show me which three?

#50, How many continuous real-valued functions f are there with domain [-1, 1] such that (f(x))^2 = x^2 for each x in [-1, 1]?

Ans: D, Four.

Can anyone show me which four?

#61, What is the greatest integer that divides (p^4) - 1 for every prime number p greater than 5?

Ans: E, 240.

I can deduce the answer by using calculator, but no other idea by hand.

Thank you very much.