Carla's sheepdog rounded up 90% of her sheep, but the remaining 10% wandered off into the hills. If there are 81 sheep in the pen, how many are out in the wilderness?
First find the total number of sheep by dividing the number rounded up by 90%: 81 sheep / .9 = <<81/.9=90>>90 sheep
Then multiply that number by 10% to find the number that are in the hills: 90 sheep * 10% = <<90*10*.01=9>>9 sheep
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