If Katy has 1 3/8 cups of flour and her recipe calls for 2 cups, how much more flour does she need?

To determine how much more flour Katy needs, we start with the amount she has, which is 1 3/8 cups, and subtract this from the amount her recipe requires, which is 2 cups.

First, it's useful to convert the mixed number (1 3/8) into an improper fraction. This can be done by multiplying the whole number by the denominator and adding the numerator:

1 (whole number) × 8 (denominator) + 3 (numerator) = 8 + 3 = 11.

Thus, 1 3/8 can be expressed as 11/8.

Now we have 2 cups, which can also be expressed as a fraction. In terms of eighths, 2 cups is 16/8 (since 2 × 8 = 16).

Next, we subtract the amount of flour Katy has from the amount she needs:

16/8 (needed) - 11/8 (has) = (16 - 11) / 8 = 5/8.

Therefore, Katy needs 5/8 more cups of flour to meet the recipe's requirements. This is why the correct answer is indeed 5/8 cup.