Measuring 9 minutes from 2-hour glasses Puzzle

Measuring 9 minutes from 2-hour glasses puzzle

Using only a Four-minute hourglass and a seven-minute hourglass,
How will you measure exactly nine minutes?
Restriction:- Without the process taking longer than nine minutes.

Solution

We measure 7 Minute from One Hourglass. We reverse it at 7th minute
And, 4+4=8 Minutes from Second Hourglass         –   8 Minutes
8(from 1)-7(From 2) = 1 Minute                                     –   1 Minutes
TOTAL = 9 MINUTES

EXPLANATION-
0 Minutes – Start both hourglass at the same time.
4 Minutes – The four minute glass runs out. Flip the four minute glass.
7 Minutes – The seven minute glass runs out. Flip the seven minute glass.
8 Minutes – The four minute glass runs out; the seven minute glass has been running for one minute. Flip the seven minute glass.
9 Minutes – The seven minute glass runs out.

Using only a Four-minute hourglass and a seven-minute hourglass, How will you measure exactly nine minutes?

Detailed Solution

Using only a Four-minute hourglass and a seven-minute hourglass, How will you measure exactly nine minutes?
0 Minutes – Start both hourglass at the same time.
Using only a Four-minute hourglass and a seven-minute hourglass, How will you measure exactly nine minutes?
4 Minutes – The four minute glass runs out. Flip the four minute glass.
Using only a Four-minute hourglass and a seven-minute hourglass, How will you measure exactly nine minutes?
7 Minutes – The seven minute glass runs out. Flip the seven minute glass.
Using only a Four-minute hourglass and a seven-minute hourglass, How will you measure exactly nine minutes?
8 Minutes – The four minute glass runs out; the seven minute glass has been running for one minute. Flip the seven minute glass.
Using only a Four-minute hourglass and a seven-minute hourglass, How will you measure exactly nine minutes?
9 Minutes – The seven minute glass runs out.