Quadratic Equations and Common Roots

XAT 2018 · Quantitative Ability & Data Interpretation · Medium · Quantitative Aptitude

Two different quadratic equations have a common root. Let the three unique roots of the two equations be A, B and C - all of them are positive integers. If (A+B+C)=41(A + B + C) = 41 and the product of the roots of one of the equations is 35, which of the following options is definitely correct?

  1. A.

    The common root is 29.

  2. B.

    The smallest among the roots is 1.

  3. C.

    One of the roots is 5.

  4. D.

    Product of the roots of the other equation is 5.

  5. E.

    All of the above are possible, but none are definitely correct.

Answer

C

Explanation

Product of roots of one equation is 35. Since roots are positive integers, the pair is either (5,7)(5, 7) or (1,35)(1, 35). Case 1: Roots are 5,75, 7 and CC. 5+7+C=41  ⟹  C=295 + 7 + C = 41 \implies C = 29. The roots are 5,7,295, 7, 29. Case 2: Roots are 1,351, 35 and CC. 1+35+C=41  ⟹  C=51 + 35 + C = 41 \implies C = 5. The roots are 1,35,51, 35, 5. In both cases, 5 is always one of the three roots.

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