Piggy Bank: Geniuses Only

A girl liked to collect money in a piggy bank. She bought pink colored piggy bank when she was 10 years old. She put $250 in the box on each of her birthday. Her younger sister took $50 out of her piggy bank on her birthday. The girl died when she was 50 years old due to an incurable disease. When the piggy bank was opened, it had just $500.

How can that be possible?

Rack ur Brain*study*