Puzzle 018: 10 Lamps

ナゾ０１８　１０本の街灯
深夜の道路に１０本の街灯が並んで
光っている。
実は不良品お電球を使っていたらしく
２時間に１つの割合で電球が切れる。
一方、３時間ごとに見まわりが現れて、
１つだけ電球を取り替えていく。
１２時間後には、いったい何本の街灯が
点灯しているだろう。

Google Translate
10 late-night road street lights that lined the book shines. Your generous with defective light bulbs actually run out of two hours at a rate of one light bulb. Meanwhile, look around should come up every three hours, only one will replace one light bulb. After 12 hours, the street lights would have illuminated this gas.

Notes on Puzzle
A puzzle about 10 street lamps at night. Every two hours, one of the lamps will burn out. Every 3 hours, someone will come by and replace a burnt out lamp. After 12 hours, how many lamps will still be burning?