There are 21*2=<<21*2=42>>42 polar bears

So the total 21+42=<<21+42=63>>63 total animals

# Answer

63
<|im_start|>system
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<|im_start|>user
A zoo has 21 penguins and twice as many polar bears?  How many total animals do they have?
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
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user
63
A zoo has 21 penguins and twice as many polar bears?  How many total animals do they have?
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