This year, a woman has a lucrative one-year position. During this year, she will give a fraction f of her salary to her husband, a private investor, to invest and they will live this year on the remainder. Through investments, her husband can turn each dollar she gives him into 1 + r, which will be deposited in a bank account. Their goal is to save & invest enough money so they can live off this money for two years following the end of the wife's position. Toward this end, they want to choose f such that the amount in the account at the end of the year is twice what they lived off this year. In terms of r, what should f be?
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A$$\frac{1}{r+1}$$
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B$$\frac{2}{r+2}$$
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C$$\frac{2}{2r+1}$$
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D$$\frac{2}{r+3}$$
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E$$\frac{2}{2r+3}$$
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正确答案: D