Rosa's rule of thumbAunt Rosa put one hundred pretend coins on the table and asked Mina how she would split them. Then she shared a handy rule of thumb. It is called fifty, thirty, twenty. Think of ten blocks, split into five, three and two. Fifty coins cover needs, like food, a home and the bus. Thirty coins are for wants, like fun, treats and presents for friends. Twenty coins go into saving. Fifty, thirty and twenty make one hundred. A rule of thumb is a quick guide, and it is not a law. No one split fits everyone: some families need more for needs, and others save more. Then Rosa tried it on Mina's month of forty coins. She cut forty into ten blocks of four. Five blocks made twenty for needs, three blocks made twelve for wants, and two blocks made eight for saving. Twenty, twelve and eight made forty, so the rule shrank to fit Mina's month.