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たびたびお手数ですが、よろしくお願いします。
A trustee invested a total of $100,000, more than half of which was invested at 6 percent simple annual interest and the rest of which was invested at 8 percent simple annual interest. What amount was invested at 8 percent?
(1) The total annual income on the investment was $6,800.
(2) If twice as much had been invested at 8 percent and the rest at 6 percent, the total annual income on the investment would have been increased by $800.
正解はＤ
(1)がsufficientであることは分かるのですが、（2）が分かりません。例によってこれも文がよく解釈できません。
If A, B, S, and T are real numbers and the two roots of equation x2乗 + Ax + B = 0 are S and T, is ST negative?
(1) A is negative.
(2) B is negative.
正解はＢ
これはお手上げです。
二次方程式の解の公式などを使うのでしょうか？
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