you have a 5 minute hourglass and a 9 minute hour glass. How can you use them to time a 13 minute barbeque?
Start both at the same time. When the 5 min is done, you have 4 min left on the larger glass, start the bbq. When that hourglass is done, flip it over for the next nine min.
4+9=13
To time a 13-minute barbeque using a 5-minute and a 9-minute hourglass, you can follow these steps:
1. Start both hourglasses simultaneously.
- Flip both the 5-minute and the 9-minute hourglass so that the sand starts flowing.
2. Let the 5-minute hourglass run out completely.
- Once the sand in the 5-minute hourglass finishes, it indicates that 5 minutes have passed.
3. While the 5-minute hourglass is running, 8 minutes will have passed in the 9-minute hourglass (since their combined time is 5 minutes + 8 minutes = 13 minutes in total, which is the desired cooking time).
4. As soon as the 5-minute hourglass is completed, immediately flip it over again to start measuring the remaining time.
5. Wait until the remaining 4 minutes in the 9-minute hourglass run out.
- The 9-minute hourglass is now empty, signaling that 13 minutes have passed.
By following these steps, you can effectively measure a 13-minute barbeque using a 5-minute and 9-minute hourglass.