Minimum Value of Algebraic Expression

CAT 2020 Slot 2 · QA · Hard · Algebra

If xx and yy are positive real numbers satisfying x+y=102x + y = 102, then the minimum possible value of 2601(1+1x)(1+1y)2601 \left(1 + \frac{1}{x}\right)\left(1 + \frac{1}{y}\right) is

Answer

2704

Explanation

Expand the expression: E=2601(1+1x+1y+1xy)=2601(1+x+yxy+1xy)E = 2601 \left(1 + \frac{1}{x} + \frac{1}{y} + \frac{1}{xy}\right) = 2601 \left(1 + \frac{x+y}{xy} + \frac{1}{xy}\right) Since x+y=102x + y = 102, xyxy is maximized when x=y=51x = y = 51. Max value of xy=51×51=2601xy = 51 \times 51 = 2601. To minimize EE, we need to minimize 103xy+1\frac{103}{xy} + 1, which occurs when xyxy is maximum, i.e., xy=2601xy = 2601. Substitute xy=2601xy = 2601: Emin=2601(1+1022601+12601)=2601+102+1=2704E_{\text{min}} = 2601 \left(1 + \frac{102}{2601} + \frac{1}{2601}\right) = 2601 + 102 + 1 = 2704

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