To determine which scale drawing represents a dilation that decreased the size of the original object, we need to analyze the scale ratios provided for each figure.
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Figure 1 (Star): Scale 1:5 means that the image is 1/5 the size of the original. This is a reduction.
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Figure 2 (Octagon): Scale 2:0.5 means that the image size is 2 times larger than the scale of 0.5 when compared to the original. This is technically an increase since we can think of it as a ratio of sizes (2/0.5 = 4), making this larger.
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Figure 3 (Triangle): Scale 10:1 means that the image is 10 times larger than the original. This is also an increase.
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Figure 4 (Pentagon): Scale 1:0.1 means that the image is 1/0.1 or 10 times larger than the original. This is an increase too.
Based on this analysis, Figure 1 (Star) is the only one that represents a dilation that decreased the size of the original object.