Monday puzzle: science experiment
This is a puzzle that my cousin sent to me that I really enjoyed:
A chemistry teacher offers his class an experiment for extra credit. To complete the lab, students are to keep bacteria in a special chamber for exactly 9 minutes.
The sadistic part is the teacher only gives the students a 4-minute and a 7-minute hourglass with which to measure time. There are no other time-measuring instruments, as wristwatches and cell phones are confiscated.
To complete the lab, the bacteria can be stored in small intervals of time, but the total time that it should be in the chamber must be 9 minutes.
Extra credit will only be awarded to the student or students that complete the lab first.
What is the shortest time the experiment can be completed?
A) 9 minutes
B) 12 minutes
C) 18 minutes
D) 21 minutes
Can you solve it? Give it a try before reading the answer in the comments section.
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