s91arvindh wrote:5 boys and 5 girls (5 pairs of brother and sister) are arranged randomly in a row. What is the probability
- all boys are together
all boys and all girls are together
all siblings are together
all siblings are not together
I am trying to solve the above questions but stuck somewhere .[/list]
Here are some quick answers for the others:
1:: All the boys together.
Treat the five boys as ONE person, and each of the girls as ONE person. That means we have 6 "people" to arrange, which gives us 6!. Then, the five boys must be arranged amongst themselves, so that gives us another 5! possible arrangements, so we have 6! * 5!. (If it's a probability question, make sure the denominator is 10!)
2:: All the boys together and all the girls together.
Treat the five boys as ONE person, then the five girls as ONE person. That means we have two "people" to arrange, or 2!. Then, we have the arrange the boys amongst themselves (5!) and the girls amongst themselves (5!), so we have 2! * 5! * 5!. (If it's a probability question, make sure the denominator is 10!)
3:: All the siblings together.
I did this one in my last post (above).
4:: All the siblings NOT together.
Not quite sure I understand this. Is this NO sibling sitting next to his or her sibling, or is this AT LEAST ONE sibling not sitting next to his or her sibling?
