How many Jews were at the death camps?
About 1.8-2 million Jews were killed in open air shootings (mainly in the former Soviet Union) and by being forced to live in intolerable conditions in ghettos. About 4 million were killed in extermination and concentration camps, by forced labour and gassing. The number of survivors (in the sense of people actually taken to camps who emerged alive when they were liberated) was very small. So, the to your question is: about 4 million (but obviously not all at the same time).
