At Mariah's birthday party, 9 of her friends ate 3/4

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

If 9 friends ate 3/4 of the cake, you can find the amount of cake each friend ate by dividing 3/4 by 9.

(3/4) / 9 = 3/4 * 1/9 = 3/36

Therefore, each friend ate 3/36 of the cake.