Ruth Doris (Gimbel) Koidan, age 87, died September 12, 2018 at Cedar Glen Assisted Living in Rockville, Maryland. She was the beloved wife of the late Walter Koidan. She held a PhD in mathematics and taught at universities in the Washington, D.C. area. Ruth was a lover of classical music, an avid dancer, and enjoyed the outdoors. She is survived by several nieces and nephews who are scattered around the country. There will be no service.