1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Probability of 2 items not next to each other

  1. Jul 24, 2014 #1
    1. The problem statement, all variables and given/known data

    i am having problem on part e , the ans given is 504-(7c1 X4 )= 476

    but my working would be 504-(7c1 X4 x2 )= 448

    since the pure maths and statistics can be arranged in 2! ways , but the 1 tem which is chosen from 7 items can be placed in 4 location , just as in the picture.

    2. Relevant equations

    3. The attempt at a solution

    Attached Files:

  2. jcsd
  3. Jul 24, 2014 #2


    User Avatar
    Science Advisor

    I have no idea what you mean by "but the 1 tem which is chosen from 7 items can be placed in 4 locations". (c) and so (e) refer to choosing 3 items out of 9. There are NO "4 locations".
    How many different ways are there to choose 3 items out of 9 and then place them in some order? (i.e. part (c)). How many of those involve choosing the pure math and statistics text. How many of those have the two texts as first and second or as second and third? Subtract the second answer from the first.
  4. Jul 24, 2014 #3

    D H

    User Avatar
    Staff Emeritus
    Science Advisor

    The answer in the book is correct.

    Your "4x2" doesn't make sense. Consider three items, labeled A, B, and C, and arranged in a line. Some of the arrangements have items A and B adjacent, others don't. The total number of arrangements is 3!=6. The number in which items A and B are adjacent has to be less than this.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted