数

1. Origins, structure, and basic meaning

• Structure: 数(かず) is a noun for the quantity of people or things or for a number represented in writing.
• Basic usage: A quantity appears in 参加者の数, while written numbers appear in 黒板に書かれた数.

2. Common pitfalls and similar expressions

• Quantity and written number
  • Context distinguishes how many people or things there are from numerical values written where they can be read.
• Connecting the counted group
  • The pattern 参加者の数 uses の after the relevant group to state whose or what number is meant.