种植睡莲
Growing Lily Pad
题目详情
池塘里漂浮着一朵睡莲。睡莲的面积每天都会增加一倍，直到覆盖整个池塘。单片睡莲需要30天的时间才能覆盖整个池塘。如果我们第一天用 8 片睡莲叶开始，需要多少天才能覆盖整个池塘？
There is a single lily pad floating in a pond. Everyday, the lily pad doubles in area until it covers the entire pond. It takes exactly 30 days for the single lily pad to cover the entire pond. If we instead started with 8 lily pads on the first day, how many days would it take to cover the entire pond?
解析
如果我们从 1 片睡莲开始，需要 3 天的时间才能拥有 8 片睡莲（睡莲的数量每天都会增加一倍）。从 8 片睡莲叶开始相当于从 1 片睡莲叶开始跳过了前三天的生长。因此，8 片睡莲需要比单片睡莲少 3 天的时间才能到达池塘的整个区域。由于 1 片睡莲需要 30 天，因此需要 8 片睡莲 天。
Original Explanation
If we were to start with 1 lily pad, it would take 3 days for us to have 8 lily pads (the number of lily pads doubles each day). Starting with 8 lily pads is equivalent to having skipped the first three days of growth when beginning with 1 lily pad. Thus, it will take the 8 lily pads 3 less days to reach the full area of the pond than it took a single lily pad. Since it took 1 lily pad 30 days, it will take the 8 lily pads days.