Below is an instruction that describes a task. Write a response that appropriately completes the request in Chinese. Please answer in Chinese.

### Instruction:
 一本新版几何书有450页，比旧版多230页。旧版几何书有多少页？


### Response:
 设旧版几何书的页数为x
新版几何书有2x - 230 = 450页
2x = 450 + 230
2x = 680
x = 680/2 = <<680/2=340>>340页