The Math Forum

Search All of the Math Forum:

Views expressed in these public forums are not endorsed by NCTM or The Math Forum.

Math Forum » Discussions » Math Topics » discretemath

Notice: We are no longer accepting new posts, but the forums will continue to be readable.

Topic: Combination
Replies: 3   Last Post: Oct 6, 2008 10:28 PM

Advanced Search

Back to Topic List Back to Topic List Jump to Tree View Jump to Tree View   Messages: [ Previous | Next ]
Brad Grillakis

Posts: 4
Registered: 10/2/08
Posted: Oct 6, 2008 5:37 PM
  Click to see the message monospaced in plain text Plain Text   Click to reply to this topic Reply

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?.)


part a)
nCr = n! / (r! * (n-r)!)
15C5 = 15! / (5! * (15 - 5)!)
= 15! / (5! * 10!)
= 3003

part b) I need help with?

Point your RSS reader here for a feed of the latest messages in this topic.

[Privacy Policy] [Terms of Use]

© The Math Forum at NCTM 1994-2018. All Rights Reserved.