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!

Homework Help: Expected Sequences in a Random Events

  1. Feb 22, 2010 #1
    How many heads in a row would you expect to find if you toss a fair coin 8 times?

    I am thinking that the probability of 3 heads is 1/8 and since you have 8 tosses, that would give an E(x) of 1. So I am guessing that 3 is the number of heads one would expect to see in a fair coin is tossed 8 times. But I am not sure... Any help?
  2. jcsd
  3. Feb 23, 2010 #2


    User Avatar
    Homework Helper

    You can do this in two ways, the basic method and the shorter method.

    The basic way is to use the definition of E(X)= ∑all x x*P(X=x)

    Write out in a tabular form, the distribution


    x is the number heads obtained, so x goes from 0 to 8.

    The other way is to see if the question can be fitted to a special type distribution.
  4. Feb 23, 2010 #3


    User Avatar
    Homework Helper

    I need some clarification: which question is of interest:

    1) How many heads would you expect to occur during 8 flips of a fair coin?

    2) If a fair coin is flipped 8 times, how long a sequence of consecutive heads would you expect to occur? (I phrased this from your wording "How many heads in a row...")

    These questions are not the same.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook