- At 0 minutes: Start both hourglasses at the same time.
- At 4 minutes: 4 minutes hourglass runs out and flip it. 7 minutes hourglass is left with 3 minutes.
- At 7 minutes: 4 minutes hourglass is left with 1 minute. 7 minutes hourglass runs out and flip it.
- At 8 minutes: 4 minutes hourglass runs out and 7 is filled with 6 minutes and 1 minute on the other side. Flip it as the sand is left with 1 minute.
- At 9 minutes: 7 minutes hourglass becomes empty from above side.
Hence we measured 9 minutes.
This article is contributed by Vikash Kumar. Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above