To determine how much Kathy will spend on apples, we can follow these steps:

1. Find the total weight of apples required:

   • Each apple pie requires $2 \frac{3}{4}$ pounds of apples.
   • Kathy is making 3 pies.
   • Multiply the weight for one pie by 3 to get the total weight: $2 \frac{3}{4} \times 3 = \frac{11}{4} \times 3 = \frac{33}{4} = 8.25 \, \text{pounds of apples}.$

2. Calculate the total cost:

   • The cost of one pound of apples is $2.49.
   • Multiply the total weight of apples by the cost per pound: $8.25 \times 2.49 = 20.5425 \, \text{dollars}.$

So, Kathy will spend approximately $20.54 on apples.

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Would you like more details on any part of the solution? Here are some related questions:

1. How do you multiply fractions and mixed numbers?
2. How would the cost change if the price of apples increased to $2.99 per pound?
3. What if Kathy made 4 pies instead of 3? How would that affect the total weight of apples needed?
4. How can you convert between decimals and fractions?
5. How do rounding rules apply when calculating the cost in real-world problems?

Tip: When dealing with money, it's often useful to round to the nearest cent, which means rounding to two decimal places!