Counting The Twins

A census taker in a rural area went up to a farm house and knocked. When a woman came to the door, he asked her how many children she had and their ages. She said, "Les' see now, there's the twins, Sally and Billy, they're eighteen. And the twins, Seth & Beth, they're sixteen. And the twins, Penny and Jenny, they're fourteen-- "

"Hold on!" said the census taker, "Did you get twins every time?"

The woman answered, "Heck no, there were hundreds of times we didn't get nothin'!"