In how many ways we can put 7 people in 4 double rooms in condition that 2 of them want to stay together?
i will solve this PS this way, dunno if its correct.reza_moohebat wrote:In how many ways we can put 7 people in 4 double rooms in condition that 2 of them want to stay together?
first of all i will select 2 people to arrange 4 doubles room = 4!*7!/(2!*5!)
then there are 3 room left and 5 people left, i will arrange 5 people into 3 double room....
5!/3!
so total = 4*5+24*21
dunno if its right
heheheh
