How do you measure 9 minutes with a 4 and 7 minute hourglass?

When the 4-min timer is empty for the second time, the 7-min timer has 1 minute worth of sand in the bottom half. Flip it over so there is now 1 minute in the top. When the 7-min timer empties, 9 minutes have elapsed.

How accurate is a hourglass?

Hourglasses are aesthetically pleasing ornaments, rather than accurate timepieces – most of our hourglasses (except fillable ones) are accurate to within +/- 10\%.

How do you use a four-minute and a seven-minute hourglass?

Originally Answered: Using only a four-minute hourglass and a seven-minute hourglass, measure exactly nine minutes–without the process taking longer than nine minutes. 0:00 – Start both at the same time. 4:00 – The four minute glass runs out. Flip the four minute glass. 7:00 – The seven minute glass runs out. Flip the seven minute glass.

How do you measure half way on an hourglass?

Whatever number of thumb widths it is, divide it by 2 and that will (very accurately) give you the half way point on the hourglass which will equal to 2 minutes. Once the seven minute hourglass is done, flip the 4 minute timer.

How do you count to 9 minutes on a 7 minute timer?

When the 7 minute timer is done, the 4 minute timer will have 1 minute left. Now you can count to 9 minutes by simply leaving the 4 minute to expire (1 min), flip it and let it expire (4 min), flip it again and let it expire (4 min). 1 + 4 + 4 = 9 The key is understanding that you will have to use the two hourglasses together.

How to solve the 7 hour sand puzzle?

Since this situation test our mental fortitude and problem solving skills, can we start by opening the lids and emptying the sand from the 4 min. Pour the sand from the 7 into the empty 4 so you are left with three. Poor out that three into a pile and fill the 7 min with the remains sand and repeat to get another three.