How we read and write numbers

To make it easier to read¹ large numbers, we separate the figures of the numbers by commas into groups of three, counting from right to left. Each group is called a period and has its own name.

The system of numbers we use, called Arabic system, is a decimal system: that is, it is based on tens. In this system, the value a digit represents is determined by the place² it in the number; if a digit is moved to the left one place, the value it represents becomes ten times as great³.

Zero in the decimal system is a "place-holder"; in the number 30, the zero shows that 3 has been moved to the left one place, thus counting tens instead of ones. The place value in numbers is shown below:

682,000,000,000 847,000,000 136,000 592

Billions Millions Thousands Ones

These numbers are read: six hundred eighty-two billion, eight hundred forty-seven million, one hundred thirty-six thousand, five hundred and ninety-two.

682,000,000,000 847,000,000 136,000 592

Billions Millions Thousands Ones or Units

4 periods 3 periods 2 periods 1 period

Rule to Remember. a) All periods of a number contain three digits, or places (the first period on the left may or may not). b) Zero is used as a place-holder.

Average. When we want to find a single number that will represent all the numbers in a group of unequal numbers or quantities we find the average (or arithmetic mean). To find the average of a group of unequal numbers, we add the numbers and then divide their sum by the number of addends.

Notes:

¹ to make it easier to read - для того, чтобы легче читать

² is determined by the place - определяется местом

³ ten times as great - в десять раз больше