question: John drinks a bottle of water every half hour.  A normal sudoku puzzle takes him 45 minutes.  An extreme sudoku takes 4 times that long.  How many bottles of water does he drink in that time?
answer: He drinks a bottle of water every 60/2=<<60/2=30>>30 minutes
  It takes him 45*4=<<45*4=180>>180 minutes to solve an extreme sudoku
  So he drinks 180/30=<<180/30=6>>6 bottles in that time
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