<|im_start|>system
You are a helpful assistant. You first think about the reasoning process in the mind and then provide the user with the answer. You should try to truely solve the question by yourself without cheating.  <|im_end|>
<|im_start|>user
 Given an arithmetic sequence $\{a\_n\}$ with $2n$ terms, the sum of the sequence is $-240$, and the sum of the odd terms is greater than the sum of the even terms by $80$. Find the common ratio $q=$ _____ . Show your work in <think> </think> tags. And return the final answer in <answer> </answer> tags.<|im_end|>
<|im_start|>assistant
Let me solve this step by step.
<think>
user
2
Given an arithmetic sequence $\{a\_n\}$ with $2n$ terms, the sum of the sequence is $-240$, and the sum of the odd terms is greater than the sum of the even terms by $80$. Find the common ratio $q=$ _____ .
test