# Thread: permutations and combinations

1. ## permutations and combinations

How many numbers greater than 4000 can be formed from the figures 3, 5, 7, 8, 9 (repetitions not allowed)

my working out was that

_ _ _ _

for the first place, there are 4 possibilities, for the second digit, there are still 4, for the third there are 3 and for the fourth there are 2, so i multiplied 4x4x3x2
but the answer is 216

i also went for a different approach
where there are three digits and 5 numbers to fill it
SO it becomes 5P3 where 5!/5!-3! = 60 and i multipled that by 4 cause there are 4 numbers possible for the first digit. but that gave me 240
eurghz i dont get it ! ><"" sorryy if anyone could help me i would realli realli appreciate it !!
thankyou ! =D

2. Where does it say that the numbers can only be 4 digits long?

If we look at numbers that are only 4 digits long, then yes, the number of possibilities would be
4 x 4 x 3 x 2 = 96.

But then we also have to look at 5 digit numbers, and the number of possibilities for those would be
5 x 4 x 3 x 2 x 1 = 120.

Add them together and you get 216.

01

3. omgsh thank you so much !
iloveyou =D