If $$\frac{1}{2}$$ of the air in a tank is removed with each stroke of a vacuum pump, what fraction of the original amount of air has been removed after 4 strokes?
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A$$\frac{15}{16}$$
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B$$\frac{7}{8}$$
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C$$\frac{1}{4}$$
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D$$\frac{1}{8}$$
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E$$\frac{1}{16}$$