At Mariah’s birthday party, 9 of her friends ate 3/4 of her chocolate cake. How much of the cake did each friend eat?

To find out how much cake each friend ate, we need to divide the amount eaten by the number of friends.

9 friends ate 3/4 of the cake, so each friend ate 3/4 / 9 = 1/4 * 1/9 = 1/36 of the cake. Answer: \boxed{\frac{1}{36}}.