Math Riddle: How can you measure nine minutes with have two hourglasses, one four-minute, and one seven-minute?
Answer: The correct answer is to Turn over the two hourglasses on the double. At the point when the four-minute hourglass runs out, turn it over. At the point when the seven-minute hourglass runs out, turn it over.
At the point when the four-minute clock runs out this time (eight minutes have slipped by), the seven-minute hourglass has been running for one moment. Presently turn over the brief clock back finished.
At the point when the clock runs out, nine minutes have passed.