From: Joel Pearson <lists@...>
Date: 2013-05-16T08:12:28+09:00
Subject: Re: n00b looking to learn from the best

I'd skip the mapping and just use inject...

def lassy_sum( numbers )
  numbers.each.with_index.inject(0) do |sum, (num, idx)|
    sum + num * idx
  end
end

Depending on what you mean by the position in the array, you might want 
"num * ( idx + 1 )", otherwise you'll always get 0 for the first

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