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Re: Which one of the following is the minimum value of the sum of two [#permalink]
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SajjadAhmad wrote:
Which one of the following is the minimum value of the sum of two integers whose product is 36?
(A) 37
(B) 20
(C) 15
(D) 13
(E) 12


\((a-b)^2 \geq 0 \iff (a+b)^2 \geq 4ab \iff a+b \geq 2\sqrt{ab} \quad \forall a,b>0\)

Hence \(a+b \geq 2\sqrt{ab} =2\sqrt{36} =12 \iff a=b=6\)

The answer is E

Mathematically, AM-GM inequality is defined that: \(x+y \geq 2\sqrt{xy} \quad \forall x,y \geq 0\)
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Re: Which one of the following is the minimum value of the sum of two [#permalink]
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SajjadAhmad wrote:
Which one of the following is the minimum value of the sum of two integers whose product is 36?
(A) 37
(B) 20
(C) 15
(D) 13
(E) 12

Source: Nova GMAT
Difficulty Level: 550



We have the following positive integers that yield a product of 36.

1 and 36

2 and 18

3 and 12

4 and 9

6 and 6

Thus, the minimum sum is 6 + 6 = 12.

Alternate Solution:

It is a well-known fact that for a given area of a rectangle, the smallest perimeter is obtained when the shape is a square. We can use this fact, noting that xy = 36 is an area formula, where x = length and y = width. Thus, since a square has length and width equal, we see that x = y, so we can have x^2 = 36, and so x = 6. Thus, the minimum sum (half-perimeter) will be 6 + 6 = 12.

Answer: E
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Re: Which one of the following is the minimum value of the sum of two [#permalink]
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Re: Which one of the following is the minimum value of the sum of two [#permalink]
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