In a zoo, there are only deer and birds. Total heads = 36 and total legs = 100. How many birds are there?

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Accepted Answer

1. Let D = deer, B = birds. Heads: $D+B=36$.
2. Legs: $4D+2B=100$.
3. From (1) $D=36-B$. Substitute: $4(36-B)+2B=100$.
4. Solve: $144-4B+2B=100 \Rightarrow -2B=-44 \Rightarrow B=22$.
5. So there are **22 birds**.
FINAL_ANSWER: d

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