Puzzle 104 - solution

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  •  Start both the timers - 11 minutes and 7 minutes. 
  • When 7 minutes timer is empty, invert it - turn it over. 
  • After 11 minute timer is empty, turn the 7 minute timer over again. (It will now act as 4 minute timer.)
  • When this 7 minute timer is empty, your 15 minutes have elapsed. 


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