Search All of the Math Forum:
Views expressed in these public forums are not endorsed by
Drexel University or The Math Forum.
|
|
|
|
Combination
Posted:
Oct 6, 2008 5:37 PM
|
|
I need help with this. I am not sure if part (a.) is correct and was wondering if anybody can check that? Also part (b) I need help with. thanks Brad.
Consider 15 identical toothpicks arranged parallel to each other in 15 distinct spots:
|||||||||||||||
a.) How many ways are there to choose 5 of these toothpicks? (Hint: one example of a valid choice of 5 toothpicks would be ?first, third, ninth, tenth, twelfth?.)
b.) How many ways are there to choose 5 of these toothpicks if no two toothpicks can be next to each other? (Hint: one example of a valid choice is ?first, third, fifth, seventh, ninth?.)
---------------------------------------------------------
MY WORK:
part a)
nCr = n! / (r! * (n-r)!)
15C5 = 15! / (5! * (15 - 5)!)
= 15! / (5! * 10!)
= 3003
part b) I need help with?
|
|
|
|
