Answer:
As she ate 1/10 of cake, we need to know how many cake remains after it, so we can substract:
1 - 1/10 = 10/10 - 1/10 = 9/10
Then, we need to divide the 9/10 into 3 portions:
(9/10) / 3 = 9/30 = 3/10
So we know the fractions would be 3/10 each on this situation..