Find out what birthday gift a young boy decides to buy his grandfather after saving his allowance and exploring his options through calculating percentages. Grandpas Birthday Present covers additional topics including budgets, estimation, and managing and saving money as well as specific strategies to help readers understand percent.Find out what birthday gift a young boy decides to buy his grandfather after saving his allowance and exploring his options through calculating percentages. Grandpas Birthday Present covers additional topics including budgets, estimation, and managing and saving money as well as specific strategies to help readers understand percent.