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: 234,845,021,349,123,653,459 The following list breaks this number down into periods. Quintillions 234 Quadrillions 845 Trillions 021 Billions 349 Millions 123 Thousands 653 Ones 459 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, one hundred twenty-three million, six hundred fifty-three thousand, three hundred fifty-nine.” 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.