Hi guys, i have no idea how the Permutation should be used. An example, Find the number of arrangement of all nine letters of the word SELECTION in which a)the two letters E are next to each other Well i can solve this, i just make the EE as one unit so 8P8 b)the two letters E are not next to each other I don't know how i should solve this, why couldn't i take 9P9 - 8P8 . It make sense to me, take away all those that the EE are together. Also when its 9P8 what does it means? Is it like there's 9 space and you gonna put 8 things? Because i was taught that 10C3 means 10 choose 3.