If you have a 7-minute hourglass and an 11-minute hourglass, how can you boil an egg in exactly 15 minutes?

Question

Cloe Noble

Advanced Placement (AP)

3 March, 10:25

If you have a 7-minute hourglass and an 11-minute hourglass, how can you boil an egg in exactly 15 minutes?

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Answers (1)

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German Oconnell · Answer 1

To boil the egg in exactly 15 minutes, follow these steps.

1. Start both hourglasses as you start boiling the egg.

2. After the 7-minute hourglass runs out, turn it to start it again.

3. Four minutes later, when the 11-minute hourglass runs out, turn the 7-minute hourglass again.

4. Wait for the 7-minute hourglass to run out, which will take another four minutes and get you to exactly 15 minutes of boiling time.