Lesson Logic problems - The solution to Problem 5

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The solution to Problem 5

Below (after the reminder) is the solution to the Problem 5 of the lesson Some logic problems (the topic Miscellaneous word problems
of the section Word problems in this site).

Problem 5 formulation (reminder)
It takes 15 minutes to boil an egg.
How could you boil the egg having two hourglasses that measure 7 and 11 minutes?

Solution
Start running both 11-minutes and 7-minutes hourglasses simultaneously.
When the 7-minutes hourglass emptied, start to boil the egg.
When 11-minutes hourglass emptied (after 4 minutes!), turn it over and run again. Continue to boil the egg.
When 11-minutes hourglass emptied again, boiling the egg is completed (because 4 + 11 = 15).

Answer
Start running both 11-minutes and 7-minutes hourglasses simultaneously.
When the 7-minutes hourglass emptied, start to boil the egg.
When 11-minutes hourglass emptied, turn it over and run again. Continue to boil the egg.
When 11-minutes hourglass emptied again, boiling of the egg is completed.

Back to the original lesson Some logic problems (the topic Miscellaneous word problems of the section Word problems in this site).

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