Mrs. Keegan, Mrs. Todd, Mrs. Fowler, and Mrs. Duncan split 5/8 of a cake. How much cake does each teacher get?

To find the amount of cake each teacher gets, we need to divide 5/8 (the amount of cake they split) by the number of teachers, which is 4.

Therefore, each teacher gets 5/8 / 4 = 5/8 * 1/4 = 5/32 of a cake. Answer: \boxed{\frac{5}{32}}.