You have two hourglasses: A 7 minute one and an 11 minute one. Using just these 2 hourglasses, accurately time 15 minutes.
A more wordy version of this - A baker has only 2 timers that can measure 7 minutes and 11 minutes. How can he set a timer for 15 minutes to bake a cookie?
Level:EASY
2 comments:
Start both the hourglasses simultaneously. When the 7 min. timer gets over, the 11 min. one will have 4 min. left in the top compartment and 7 in the bottom one. Turn only the 7 min. one upside-down. Now, when the 11 min. gets over, 4 min. will have elapsed. Thus, the 7 min. one will have 4 in the lower compartment and 3 in the upper which are left. Now immediately turn upside down the 7 min. timer which has 4 min. left in the lower compartment. Thus the baker will have accurately timed 15 minutes to bake the cookie.
quite easy.
The answer is correct
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