## Problem 18 of Monte Carlo solutions to Fifty Challenging Problems...

(This is another part of the Fifty Problems series, a set of example applications of Monte Carlo methods. In each post, I present source code which answers a probabilistic question using simulated models of the underlying system.)

Problem 18: What's the probability of getting 50 tails in 100 toin cosses?

#!/usr/bin/env ruby
# This is pretty straightforward:
# we just count the # of 50s we get.
TRIALS=1000000
n_fifties = 0
TRIALS.times do
heads = 0
100.times { heads += rand(2) }
n_fifties += 1 if 50 == heads
end
puts "Out of #{TRIALS} trials"
puts " we got #{n_fifties} even splits, so "
puts " P=#{n_fifties/TRIALS.to_f}"

I've been coding my way through *Fifty Challenging Problems in Statistics with Solutions*. This post is a part of the *Fifty Challenging Problems* series.

*This was brought to you by Josh Myer.* He has other
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