Prof. Blanchard used an unique way to measure time for a test lasting 15 minutes.
He used two hourglasses, one measuring 7 minutes and the other measuring 11 minutes.
How did he measure the 15 minutes by turning the hourglasses a minimum number of times?

Seven minutes before the test, start both hourglasses. When the 7 runs out, flip the 11 and start the test. When the 11 runs out after 4 min, flip it again.

Posted by Steven Lord on 2022-07-04 07:14:59