Final answer:
Isabelle could calculate the difference in the amounts spent by computing the total cost for each week and then subtracting the second week's total cost from the first week's. The expression to represent this would be (2a + 3r) - (a + 2r), which simplifies to a + r.
Step-by-step explanation:
To calculate the difference in the amounts spent on apples and oranges between the two weeks, Isabelle would need to perform the following steps:
Compute the total cost for each week: for the first week it would be (2 bags of apples × cost per bag of apples) + (3 bags of oranges × cost per bag of oranges), which is 2a + 3r. For the second week, the total cost would be (1 bag of apples × cost per bag of apples) + (2 bags of oranges × cost per bag of oranges), which is a + 2r.
Subtract the second week's total cost from the first week's total cost to find the difference: (2a + 3r) - (a + 2r).
Simplify the expression to get the final result: a + r. This represents the difference between the amounts Isabelle spent each week.