I'm having a lot of trouble with permutations and combinations, so I was hoping someone here could help me out with a few questions. Please make sure that you explain your working; I really want to understand this topic... The first question asks;

A queue has 4 boys and 4 girls standing in line. Find how mant different arrangements are possible if;

a) The boys and girls alternate.

b) 2 particular girls wish to stand together.

c) All the boys stand together.

d) Also find the probability that 3 particular people will be in the queue together if the queue forms randomly.

EDIT: If it's any help, here are the answers...

a) 1152

b) 10080

c) 2880

d) 3/28

EDIT: I've got a new problem now;

A table has 4 boys and 4 girls sitting around it.

a) Find the number of ways of sitting possible if the boys and girls can sit anywhere around the table.

b) If the seating is arranged at random, find the probability that;

i) 2 particular girls will sit together.

ii) All the boys will sit together.