Finn watches 11 tadpoles swimming in the pond.  Suddenly he sees 6 of them come out of hiding from under a lily pad ,then he sees 2 of them hide under a rock.  How many tadpoles can Finn see in the pond now?
When the hidden tadpoles come out, Finn sees 11 + 6 = <<11+6=17>>17 tadpoles swimming.
After some of them hide under a rock, he now sees 17 - 2 = <<17-2=15>>15 tadpoles swimming.
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