Solution Step 0/0
Using hourglasses - a 4-min and a 7-min - measure out exactly 9 minutes.
Which of the two hourglasses will you turn upside-down more times while accomplishing the task?
Which of the two hourglasses will you turn upside-down more times while accomplishing the task?
Explanations
1. Set both hourglasses simultaneously.2. In the moment the 4-min hourglass ends its countdown, turn it upside down. The first 4 minutes passed. 3 more minutes of sand are still left the upper half of the 7-min hourglass.
3. After those 3 minutes of sand from the 7-min hourglass are completed, turn the 7-min hourglass upside down. 1 more minute of sand is still left in the 4-min hourglass. We are at 7 minutes as of this moment.
4. Now the remaining 1 minute in the upper half of the 4-min hour glass brings us to the 8 minute mark.
5. In the moment we reach the 8 minute mark (all sand in the 4-min hourglass is in its bottom half), immediately turn once again the 7-min hourglass. 1 minute of sand collected in its bottom half will be enough to reach our goal 9 minute mark.
The 4-min hourglass is turned upside down once and the 7-min hourglass - twice while completing the challenge.
Check The 4-min one
Check The 7-min one
Check Same for each
Check Neither one
