To determine which assumption Sara made about the starting balance on her gift card, we first need to calculate the total amount she spent at the bakery.
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Calculate the total cost of the muffins:
- 6 muffins at $0.45 each: \[ 6 \times 0.45 = 2.70 \]
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Calculate the total cost of the cookies:
- 2 boxes of cookies at $2.70 each: \[ 2 \times 2.70 = 5.40 \]
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The cost of the coffee cake is:
- $3.72
Next, we add these amounts together to find the total amount spent:
\[ 2.70 + 5.40 + 3.72 = 11.82 \]
Now, since Sara estimates she has $8.00 left on her gift card, we can determine the total amount on the gift card before she made her purchases by adding the amount spent to the amount left:
\[ 11.82 + 8.00 = 19.82 \]
This indicates that the gift card started with an amount that should cover the total spending and the remaining balance. Among the possible options (A, B, C, D), the only assumption that would satisfy this requirement is a starting amount of $20.00 (since it is common to round to whole dollar amounts when dealing with gift cards and cash).
Therefore, the correct answer is:
D. The gift card started with $20.00.