Bob and Sarah each cut their sub sandwich into fifths. They each ate about half of their sandwich, but ate a different number of pieces. How many pieces of their sandwich did each person eat?

Let's assume Bob ate x pieces of the sandwich and Sarah ate y pieces of the sandwich.

Since they each cut their sandwich into fifths, and each ate about half of their sandwich:

Bob ate \frac{1}{2} \times 5 = \frac{5}{2} = 2.5 pieces of the sandwich.

Sarah ate \frac{1}{2} \times 5 = \frac{5}{2} = 2.5 pieces of the sandwich.

Since they ate a different number of pieces, we know that x and y are different. The only two possibilities are:

Bob ate 2 pieces and Sarah ate 3 pieces

OR

Bob ate 3 pieces and Sarah ate 2 pieces.

So, Bob ate 2 pieces and Sarah ate 3 pieces (x = 2 \text{ and } y = 3) , or vice versa.

Answer:

\boxed{\text{Bob ate 2 pieces and Sarah ate 3 pieces, or vice versa}}