1)What is the probability of getting exactly half the questions on a ten question True/False test by guessing?

A: 63/256 how do you get that answer?

2)How many ways are there to assign grades of A,B,C,D,E to each of the nine students in a class so that exactly 4 of the students get grades above C.

A:489,888

3)How many ways are there to arrange the letters in denounced as follows?

a) there are no restrictions

b) the consanants are all adjacent

c) No two of the vowels are adjacent

A:

a)45360

b)1800

c)5400

If anyone has any idea how to arrive at these answers please respond. I have been stuck on these for 2 days now.