When you write a long number, you use commas to separate periods. Periods are simply groups of three numbers. They help make long numbers more readable. For example, here’s about as long a number as you’ll ever see:

234,845,021,349,230,467,304

The following list breaks this number down into periods.

Quintillions | 234 |

Quadrillions | 845 |

Trillions | 021 |

Billions | 349 |

Millions | 230 |

Thousands | 467 |

Ones | 304 |

This list helps you read the number. Begin all the way to the left and read, “Two hundred thirty-four quintillion, eight hundred forty-five quadrillion, twenty-one trillion, three hundred forty-nine billion, two hundred thirty million, four hundred sixty-seven thousand, three hundred four.”

When you read and write whole numbers, don’t say the word *and*. In math, the word *and* means you have a decimal point. That’s why when you write a check, you save the word *and* for the number of cents, which is expressed as a decimal or fraction.