Answer:
5/6 a pan of brownies.
Explanation:
2 1/2=5/2, So you have 5/2 pans of brownies. If your sister eats 1/3 of these brownies we can write the equation 5/2*1/3=b=5/6, with variable b being how much of a pan of brownies your sister has eaten. Your sister has eaten 5/6 a pan of brownies.