The squirrel split the 210 acorns into thirds, so it had 3 piles of 210 / 3 = <<210/3=70>>70 acorns.
It took 70 - 60 = <<70-60=10>>10 from each pile.
The squirrel will have 3 * 10 = <<3*10=30>>30 acorns to eat at the beginning of spring.
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