user: please explain and justify why it's £55 to Exeter on 22 Nov and £135 for same journey on 22 Dec. Many thanks in advance.
agent: Hi there Luke. What date and trains are you looking at specifically please? - Josh
user: Cambridge to Exeter st David's. Around 8am.
agent: 1/2Pricing does vary on advance tickets as they are first come first serve, so when the cheaper tickets have sold only standard fares remain 2/2 I can see a single on the 08.15 for 22/11/2017 priced at £34.00 and a fare for £43.00 on the same train but for the 22/12/2017 - Josh
user: Try it for a return journey coming back on 27th.
agent: What sort of time are you looking to travel? - Josh
user: Ideally around 8am.
agent: There isn't as much advance fare availability around Christmas as we expect it to be a busy time for travelling. -Andy
user: And around midday on return journey on 27th. So you nearly triple the price? That's thoughtful. And also - after paying £135, I'm told that it's not possible to even reserve a seat on the return journey.
agent: What time are you travelling? As our trains are running from Marylebone instead of Paddington reservations not possible on all. -Andy

Customer is enquiring about why the Price variation for the same journey but different dates. Agent informed that Pricing does vary on advance tickets as they are first come first serve,So when the cheaper tickets have sold only standard fares remain.
### Instruction: Below is a conversation between a human and an AI agent. Write a summary of the conversation.

### Input:
user: please explain and justify why it's £55 to Exeter on 22 Nov and £135 for same journey on 22 Dec. Many thanks in advance.
agent: Hi there Luke. What date and trains are you looking at specifically please? - Josh
user: Cambridge to Exeter st David's. Around 8am.
agent: 1/2Pricing does vary on advance tickets as they are first come first serve, so when the cheaper tickets have sold only standard fares remain 2/2 I can see a single on the 08.15 for 22/11/2017 priced at £34.00 and a fare for £43.00 on the same train but for the 22/12/2017 - Josh
user: Try it for a return journey coming back on 27th.
agent: What sort of time are you looking to travel? - Josh
user: Ideally around 8am.
agent: There isn't as much advance fare availability around Christmas as we expect it to be a busy time for travelling. -Andy
user: And around midday on return journey on 27th. So you nearly triple the price? That's thoughtful. And also - after paying £135, I'm told that it's not possible to even reserve a seat on the return journey.
agent: What time are you travelling? As our trains are running from Marylebone instead of Paddington reservations not possible on all. -Andy

### Response:
Customer is enquiring about why the Price variation for the same journey but different dates. Agent informed that Pricing does vary on advance tickets as they are first come first serve,So when the cheaper tickets have sold only standard fares remain.