動動腦-3

這裡有兩個沙漏, 一個是7分鐘的, 一個則是11分鐘的.

現在你要用這兩個砂漏計時15分鐘煮一顆水煮蛋, 請問怎麼辦到?

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

1. Start both hourglasses as you start boiling the egg.
2. After the 7-minute hourglass runs out, turn it over 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.

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答案:

第一步: 開始開火煮蛋的同時, 用兩個砂漏同時計時.

第二步: 待7分鐘的砂漏結束, 馬上把它倒過來繼續計時.

第三步: 4分鐘後, 11分鐘的砂漏會漏完, 此時再把7分鐘的再倒過來.

第四步: 待7分鐘的砂漏漏完(也就是4分鐘), 水煮15分鐘的蛋就完成了.