Nice. This is sad but a true look and true statistics about society in Vietnam. In fact, I think in the urban areas in Vietnam such as HaNoi, Ho Chi Minh city,etc would have a higher average wage. Just think about it, with $1 or 21,000VND, you are not able to survive.
Part time job in Vietnam normally you would have earn 10cent/hour. While in USA, AUS, UK the minimum wage are US$7, AUS$12, 6pound, respectively (per hour).
So it means that if you only have a part time job in Vietnam, you would never ever survive. But in many countries, part time job is enough for normal livings, for food and basic physical demand of human being. But actually the difference between price in Vietnam and Australia for example is very huge. For instance, a bottle of water would be 20cent in Vietnam which is 10 times lower than in Australia.