I'll give you a 20% discount

Farmer Jones wanted to buy his neighbour's cow, but on enquiring the price he was shocked to learn it was £50.

"What", he protested, "here I am, your friend and neighbour, and you ask a price like that?"

"I'll tell you what", replied the other farmer, "seeing you are my neighbour I'll give you 20% discount."

Now Farmer Jones was not much of a scholar and he wasn't quite sure what this meant so he said "I'll think about it."

He went off down the road and was still trying to figure it out when he saw the local school-mistress coming towards him on her bicycle. He beckoned her to stop and said

"Now tell me, Miss Pugh, if I were to offer you £50, less 20% discount, what would you take off?"

Miss Pugh thought for a moment and then declared "Everything, except my ear-rings."