Skill: Write whole numbers in word form

To write a whole number in word form:

1. Separate the number into groups of three digits, starting from the right. These groups are called periods:
   • millions
   • thousands
   • ones
2. Read each group as a three-digit number.
3. Add the period name after the millions or thousands group.
4. Skip any group that contains only zeros.
5. Use hyphens in numbers such as twenty-five.

Example: Write $(406{,}025{,}018)$ in word form.

First, separate the periods:

$$406 \mid 025 \mid 018$$

• $(406)$ is in the millions period: four hundred six million
• $(025)$ is in the thousands period: twenty-five thousand
• $(018)$ is in the ones period: eighteen

Put the parts together:

$$\boxed{\text{four hundred six million twenty-five thousand eighteen}}$$

The zero in the thousands group does not mean the group is skipped, because the group contains $(25)$. A group is skipped only when all three digits are zero.