"Give me money," requested the guide.

"Certainly. Let me see, you have worked a week. I gave you five
dollars when we started out. You were to have ten dollars a week while
you were with us. That leaves five dollars due you," announced the
Professor.

"Me work week. Me want ten dollars."

"But, my man, I've already paid you five dollars, which pays you for
half of the week. Here is the five dollars for the other half. That's
all I owe you. Do you understand?"

"Si señor. But Juan work one week," protested the guide.

"Let me show him," interrupted Tad. He drew ten marks in the sand with
a stick, separating them into two groups of five. "Here are ten marks,
Juan. We'll call them ten dollars. Understand?"

"Si."

"Well, here are the first five marks in the dirt that the Professor
paid you. How many does that leave?"

"Five," gleamed the white teeth.

"Right. Go to the head of the class," interrupted Stacy.

"Chunky, you keep out of this. You'll mix him up."