Passage: Mottelson was born in Chicago, Illinois, the son of Georgia (Blum) and Goodman Mottelson, an engineer. He graduated from Lyons Township High School in LaGrange, Illinois.  He received a Bachelor's degree from Purdue University in 1947, and a Ph.D. in nuclear physics from Harvard University in 1950.

Question: When did he graduate from Purdue?
1947