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標題: Form 2 Multiple choices maths exercise [打印本頁]

作者: victorique 時間: 23-10-2011 14:42 標題: Form 2 Multiple choices maths exercise

Q.1 if a+x/b+x = c/d (c no equal to d) , then x =?

A. c/d - a/b B. a-b/c-d C. ad-bc/c-d D. bc-ad/c-d

Q.2 if a/b = c/d , which of the following must be true?

i) a/c = b/d ii) a+b/b = c-d/d iii) a-b/b = c-d/d

A. i and ii only
B. i and iii only
C. ii and iii only
D. i,ii and iii

Who can help me???? I need your help !!!!!!!!

作者: 13少 時間: 23-10-2011 16:06

Q.1 Ans is C
Sol: (a + x) / (b+x) = c/d
            d(a + x) = c(b + x)
            ad + dx = cb + cx
               (d-c)x = cb-ad
                     x = (cb - ad) / (d-c)
                     x = (ad - cb) / (c-d)

Q.2 Ans is B
Sol: i)  a/b = c/d
         ad = cb
      ad/c = b
         a/c = b/d (True)

Sol: ii) (a + b)/b = (c-d)/d
            a/b + b/b = c/d - d/d
               a/b + 1 = c/d - 1
                     a/b = c/d - 2 (False)

Sol: iii) (a-b) / b = (c-d) / d
         a/b - b/b = c/d - d/d
            a/b - 1 = c/d - 1
                  a/b = c/d (True)

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