MATH PUZZLE: Can you replace...

A farmer in the country noticed that a gentleman would fish at the lake (close to the farmer's house) and would always leave with a stringer full of fish. The fellow had a boat but a fishing pole was not to be seen.
A drunk staggers into a diner and orders a couple of eggs. The waiter, suspecting that they've run out, goes back to question the chef. "Hey, Gus, do we have any more eggs?"
Gus replies, "I ran out of fresh eggs, I only have two rotten eggs left."
The waiter says, "Give him the rotten eggs. He's so bombed he won't know the difference."
Gus scrambles up the rotten eggs and heaps on hash browns, sausage and toast. The drunk is so hungry he wolfs down the breakfast without comment. He goes to pay the cashier and asks, "Where'd you get those eggs?"
She replies, "We have our own chicken farm."
The drunk asks, "Do you have a rooster?
"No," she says.
The drunk replies, "Well, you'd better get one, because some skunk is screwing your chickens."