There he was particularly influenced by Littlewood and Ingham whose lectures he attended while taking Part III of the Mathematical Tripos. Rankin graduated in 1937 and in the same year his father became Professor of Old Testament Language, Literature and Theology at the University of Edinburgh.
Doon siya ay lalo na naiimpluwensyahan ng Littlewood at Ingham na ang mga lektura siya pumasok sa habang kumukuha Part III ng matematika Tripos. Rankin nagtapos sa 1937 at sa parehong taon ng kanyang ama ay naging Professor ng Lumang Tipan sa Wika, Literatura at Teolohiya sa Unibersidad ng Edinburgh.