**Count The Legs And Divide By Four**
She walks up to the farmer and says, "if I can guess how many sheep you have, can I take one home?" The farmer kinda chuckles to himself, and then replies, "Sure, why not?" The blonde pulls out a calculator and does a whole bunch of calculus and trig equations and comes up with a number. She says to the farmer, "There are 314 sheep out there." The farmer looks at her with a shocked expression and says, "You're right! Go take your pick". The blonde takes a few minutes to pick a sheep, waves to the farmer, and leaves.
She's sitting at home the next day when she hears a knock on her front door. She opens it and finds the farmer standing there, holding his hat. He says to her, "If I can guess your real hair color, can I have my dog back?"