How long has Rivka been at the concentration camp in The Devil's Arithmetic?
Rivka has been in the camp for a year because she is intelligent and knows how to organize, but she has lost almost all of her family.
Hannah meets a little girl named Rivka, who is about ten years old and has been in the camp for about a year. In that time, she lost most of her family. Only her brother Wolfe remains, acting more dead than alive. She tells Hannah that she knows the rules, and she knows how to survive in the camp.
“See my number? It is lower than yours. Someone with a number like mine has been here a long time. We are survivors. We can tell you things. Read the numbers. My lower number tells you I can organize things.” (ch 13, p. 115)
Rivka explains to them that they need to pay attention to what the numbers mean, so they know who is likely to survive and who is not. People with lower numbers, who have been there longer, are more likely to be helpful.