In Chapter 3 of Night, describe the first selection. How did Elie and his father survive it?

Thanks to the kindness of one of the inmates Elie and his father survive the very first selection before they even know what the word means to their survival. The prisoner demands that Elie tell the guards that he is eighteen instead of fifteen. He then tells Elie's fifty year old father that he needs to say that he is forty. Women, children, and the elderly were the first to be killed inside the walls of the camps because they were thought to be useless. When Elie and his father approached the guard they did as they were told and survived the first selection that would have sent them straight to the crematorium to be burned just like Mrs. Schachter's vision might have predicted. Dr. Mengele, the guard was pointing prisoners either left or right with his baton and when he spoke to Elie and his father, the baton pointed to left, luckily they find that left was toward survival although they were frightened at first that it was to the crematorium.