Final answer:
The pair of fractions that cannot be used to find how many pounds of nuts Mindy bought in total is 5/8 pound and 3/4 pound.
Step-by-step explanation:
The pair of fractions that cannot be used to find how many pounds of nuts Mindy bought in total is 5/8 pound and 3/4 pound.
To add or subtract fractions, the denominators must be the same. In this case, the denominators 8 and 4 do not match.
To find the total weight of nuts, Mindy needs to convert both fractions to have the same denominator.
Converting 5/8 pound to the same denominator as 3/4 pound, we get 10/16 pound. Now, we can add the two fractions: 5/8 + 10/16 = 15/16 pound.