PERT estimation calculator

pert.rb

#!/usr/bin/env ruby
#
# PERT Calculator v1.0.0
#
# To install, place this file in a directory that is in your $PATH. On
# my machine, I have ~/bin in my $PATH, so that's where `pert` lives.
#
# Example:
#
#     $ pert 0.35 0.75 1
#
#      optimistic: 0.35
#          likely: 0.75
#     pessimistic: 1.0
#            + QA: 0.11 (15%)
#           FINAL: 0.83

if ARGV.empty?
  puts "Usage: pert OPTIMISTIC_HOURS LIKELY_HOURS PESSIMISTIC_HOURS"
  exit 1
end

QA_TAX = 0.15
BOOST = 4
QUANTITY = 6

optimistic, likely, pessimistic = ARGV.map(&:to_f)
estimate = (optimistic + (BOOST * likely) + pessimistic) / QUANTITY
qa_time = estimate * QA_TAX
estimate += qa_time

[optimistic, likely, pessimistic, estimate, qa_time].map { |num| num.round(2) }

puts " optimistic: #{optimistic}"
puts "     likely: #{likely}"
puts "pessimistic: #{pessimistic}"
puts "       + QA: #{qa_time.round(2)} (#{(QA_TAX * 100).to_i}%)"
puts "      FINAL: #{estimate.round(2)}"