Sure! Here are the answers to the questions based on the passage:

1. **How many ethnic groups are there in Vietnam?**
- There are 54 ethnic groups in Vietnam.

2. **Where do the Kinh people mostly live?**
- The Kinh people mainly live in the central coastal delta, the Red River delta, the Mekong delta, and major cities.

3. **What is the population of the Tay?**
- The Tay have a population of around 1 million people.

4. **Which ethnic groups have the smallest population?**
- The ethnic groups with the smallest population are Brau, Roman, and Odu, each with several hundred people.

5. **What do most ethnic peoples mainly live on?**
- Most ethnic peoples mainly live on hunting, fishing, collecting, and a semi-nomadic lifestyle.