Pages

News: Currently the LaTeX and hidden solutions on this blog do not work on Google Reader.
Email me if you have suggestions on how to improve this blog!

Thursday 4 August 2011

Math GRE - #3

A drawer contains 2 blue, 4 red, and 2 yellow socks. If 2 socks are to be randomly selected from the drawer, what is the probability that they will be the same colour?

  • $\frac{2}{7}$
  • $\frac{2}{5}$
  • $\frac{3}{7}$
  • $\frac{1}{2}$
  • $\frac{3}{5}$

    The probability of getting 2 blue in a row is: $\frac{2}{8}\frac{1}{7}=\frac{1}{28}$.

    The probability of getting 2 yellow in a row is: $\frac{2}{8}\frac{1}{7}=\frac{1}{28}$.

    The probability of getting 2 red in a row is: $\frac{4}{8}\frac{3}{7}=\frac{6}{28}$.

    So the total probability is: \[\frac{1}{28}+\frac{1}{28}+\frac{6}{28}=\frac{2}{7}.\]

    6 comments:

    Post a Comment

    This webpage is LaTeX enabled. To type in-line formulae, type your stuff between two '$'. To type centred formulae, type '\[' at the beginning of your formula and '\]' at the end.