To find out how many ounces your friend ate, we need to calculate 1/4 of the total amount in the bag, which is 13 1/3 ounces.
First, convert 13 1/3 ounces to an improper fraction:
\( 13 \frac{1}{3} = \frac{13 \times 3 + 1}{3} = \frac{39 + 1}{3} = \frac{40}{3} \) ounces.
Now, calculate 1/4 of this amount:
\[ \frac{1}{4} \times \frac{40}{3} = \frac{40}{12} = \frac{10}{3} \text{ ounces}. \]
Now, convert \(\frac{10}{3}\) to a mixed number:
\(\frac{10}{3} = 3 \frac{1}{3} \text{ ounces}.\)
So, your friend ate 3 1/3 ounces.