Dear Economist,
I feel guilty because I paid £200 to co-host a birthday party for my five-year-old with another mother, but got at least £300 of gifts in return. As a guest, I don’t like these parties because you take two gifts in return for only one party bag. But co-hosting is surely a rational thing because you pay half and get a full complement of presents?
South London Mum

Dear SLM,