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

### Instruction:
 如果巴兹在一家餐厅买了一张有78片的披萨，然后决定按照5:8的比例与服务员分享，其中巴兹的比例是5，那么服务员吃了多少片披萨减去20？


### Response:
 服务员吃了披萨的比例是8/13=<<8/13=0.615>>0.615
所以他吃了78*0.615=<<78*0.615=48.27>>48.27片
48.27-20=<<48.27-20=28.27>>28.27