Let's forget the first pole who is set at the beginning of the mile. There's one pole at 30 meters, and the second one is located at 60 meters, etc...
One mile is about 1,609 meters,
Let's calculate 1609/30=53.6. There are 53 poles if we don't count the first one. You can also notice that 53 * 30 = 1,590 meters. After the last pole, remains 19 meters so another pole set is impossible. You have then to add the pole set at the beginning of the mile. The correct answer is 54 poles.
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