It isn't about mugging, it's just that quirky thing about maths. In real life, you can't have a man cut in half, but in maths, it's perfectly reasonable to assume that. If you're uncomfortable with those numbers, we could just change the question by doubling everything, because it's all proportional.
Having said that, if a man eats a hen in a day, 1 man will eat 2 hens in one day because each man would eat a hen in a day.
To get the answer to this sum, just divide all numbers in the above reasoning by 2, and you get your answer.
I hope that sounds more logical, but honestly, the numbers don't matter. It's only maintaining the ratio that does.