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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(1+\frac{1}{x})(1+\frac{1}{y}) is

Entered answer:

Solution

✅ Correct Answer: 2704

We need to find the minimum value of 2601(1+1x)(1+1y)2601(1+\tfrac{1}{x})(1+\tfrac{1}{y}) given that x+y=102x + y = 102.

Let us start by expanding the expression to better understand what we're working with.


2601(1+1x)(1+1y)=2601(1+1x+1y+1xy)2601(1+\tfrac{1}{x})(1+\tfrac{1}{y}) = 2601(1 + \tfrac{1}{x} + \tfrac{1}{y} + \tfrac{1}{xy})

Since x+y=102x + y = 102, we can simplify 1x+1y\tfrac{1}{x} + \tfrac{1}{y}:

1x+1y=y+xxy=102xy\tfrac{1}{x} + \tfrac{1}{y} = \tfrac{y + x}{xy} = \tfrac{102}{xy}

So our expression becomes:

2601(1+102xy+1xy)=2601(1+103xy)2601(1 + \tfrac{102}{xy} + \tfrac{1}{xy}) = 2601(1 + \tfrac{103}{xy})


To minimize 2601(1+103xy)2601(1 + \tfrac{103}{xy}), we need to maximize xyxy (since 103xy\tfrac{103}{xy} gets smaller as xyxy gets larger).


The AM-GM Inequality states: For positive numbers xx and yy, x+y2≥xy\tfrac{x+y}{2} \geq \sqrt{xy}

This means: 1022≥xy\tfrac{102}{2} \geq \sqrt{xy}

Therefore: 51≥xy51 \geq \sqrt{xy}

xy≤512=2601xy \leq 51^2 = 2601

The maximum value of xyxy is 26012601, and this happens when x=y=51x = y = 51 (equality in AM-GM occurs when the numbers are equal).


When x=y=51x = y = 51:

xy=51×51=2601xy = 51 \times 51 = 2601

Using the original form:

2601(1+151)(1+151)=2601(5251)22601(1+\tfrac{1}{51})(1+\tfrac{1}{51}) = 2601(\tfrac{52}{51})^2

=2601×522512= 2601 \times \tfrac{52^2}{51^2}

=2601×27042601= 2601 \times \tfrac{2704}{2601}

=2704= 2704


We used the fact that for a fixed sum, the product is maximized when the numbers are equal. This is a consequence of the AM-GM inequality, which is a powerful tool for optimization problems. The symmetry occurs because the optimal solution has x=yx = y.

Therefore, the minimum possible value is 27042704.

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