Maximizing Algebraic Fraction Value

XAT 2015 · Quantitative Ability & Data Interpretation · Medium · Quantitative Ability

If a,b,ca, b, c and dd are four different positive integers selected from 11 to 2525, then the highest possible value of (a+b)+(c+d)(a+b)+(c−d)\frac{(a + b) + (c + d)}{(a + b) + (c - d)} would be:

  1. A.

    47

  2. B.

    49

  3. C.

    51

  4. D.

    96

  5. E.

    None of the above

Answer

C

Explanation

Let S=a+b+cS = a + b + c. To maximize S+dS−d\frac{S + d}{S - d}, we need S−dS - d to be as small as possible (minimum 1) and S+dS + d as large as possible. Set d=25d = 25. To make denominator S−d=1S - d = 1, we need S=26  ⟹  a+b+c=26S = 26 \implies a + b + c = 26. Then numerator =S+d=26+25=51= S + d = 26 + 25 = 51. Denominator =26−25=1= 26 - 25 = 1. Maximum value =51/1=51= 51/1 = 51.

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