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| 如果你忘記伊莉的密碼,請在登入時按右邊出現的 '找回密碼'。輸入相關資料後送出,系統就會把密碼寄到你的E-Mail。 The description is clear. It meant to say that, if we take the number wrongly (in sign), and if we know that only one number is wrong, then we can figure it out by making half of the difference to match that number (but different sign).
For example, if we add 4 numbers together: 1+2+3+4 = 10. But, now, we make a mistake and only get 6. The difference is 4, and half of that is 2. So, we must have made the mistake in the sign of "2", i.e. 1 - 2 + 3 + 4 = 6. ... |
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