SOLUTION: how many 3 digit numbers divisible by 5 can be formed from 1,2,3,4,5,6 ?

Algebra ->  Permutations -> SOLUTION: how many 3 digit numbers divisible by 5 can be formed from 1,2,3,4,5,6 ?      Log On


   

Question 883536: how many 3 digit numbers divisible by 5 can be formed from 1,2,3,4,5,6 ?
Answer by LinnW(1048) About Me  (Show Source):
You can put this solution on YOUR website!
Since the 3 digit number must end in 5
we have
125
135
145
165
215
235
245
265
315
325
345
365
415
425
435
465
615
625
635
645
This enumeration gives us 20 possibilities
We could also use the permutation
formula +n%21%2F%28n-r%29%21
where n is the different elements ( 1,2,3,4,6)
and r is the number taken or 2 elements in our case
+n%21%2F%28n-r%29%21 = +5%21%2F%285-2%29%21
= +5%21%2F%283%29%21
= (5*4*3*2*1)/(3*2*1)
= 5*4
= 20