What is fifty cents plus fifty cents?

A little boy named Raghu went to school as usual. His teacher was asking questions of all the students, one by one. They were all types of questions, from art to math to English.

"Renuka," the teacher said, "please tell me, what colour do we get by mixing together red and blue?"

"Green?" asked Renuka.

"No, sorry," said the teacher. "Does anyone know the answer?"

Several students voiced forth, "Purple, purple!"

"Right! Excellent! Now, Ila, your turn," the teacher continued. "How many lines does it take to draw a square?"

Ila replied, "I know the answer! Four!"

"Correct," said the teacher. "Ajit, if your mother's sister has a baby boy, how are you related to her child?"

"We are in the same family," answered Ajit.

"That is true, but how are you related?"

"He is my aunt's son."

"Right. He is your cousin."

"Oh, yes, you are right."

Then the teacher asked Raghu, "Suppose yesterday your mother gave you fifty cents. Then, a few hours later, your father gave you fifty cents. How much will it be?"

"It will become a tennis ball," answered the little boy.

The teacher was baffled. "How can that be?" she asked.

"Since fifty cents and fifty cents make a dollar, I would immediately go and buy a nice tennis ball!"

The teacher laughed and said, "Ah, I see! Wonderful, Raghu, wonderful!" The teacher was so pleased with Raghu's answer that the next day she gave him a new tennis ball.