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Re: Gmatclub test M 05, question 15/37 [#permalink]

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14 Mar 2010, 22:01

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BarneyStinson wrote:

If x is a positive integer, is sqrt(x) < 2.5*x - 5 ?

1) x < 3 2) x is a prime number

st 1) x< 3 ==> x can be 1 or 2 x = 1 --> -2.5 > 1 .. NO x = 2 --> 0>1.414 .. NO sufficient st 2 ) x is prime .. x = 2, NO x=3 or above YES not sufficient

A

BarneyStinson wrote:

X is positive integer, sqrt(x) can still be negative.

the square roots of x are +sqrt(x) and -sqrt(x) sqrt(x) is ALWAYS POSITIVE

X is positive integer, sqrt(x) can still be negative.

1: if x>0 and x<3 then possible values 1,2 (0 is neither positive nor negative) with both values sqrt(x) < 2.5*x - 5. hence sufficient. 2: x can be 2,3,5,7,11 ..... any value of x greater than 4 will result in sqrt(x) > 2.5*x - 5 hence insufficient. Hence A.

Also sqrt of positive number is always +ve it can't be negative.

Re: Gmatclub test M 05, question 15/37 [#permalink]

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15 Mar 2010, 00:35

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sidhu4u wrote:

bangalorian2000 wrote:

Also sqrt of positive number is always +ve it can't be negative.

Sqrt of any positive number can be negative, its not necessarily to be positive. for example, if we have 9 as number, than its sqrt can be 3 or -3 since 9 = 3*3 or (-3)*(-3)

Mate just need to clarify that on Gmat Land , root of any number is +ve

i.e. root of 4 has to be taken as 2 only and not -2....

however if you are given x^2 = 4 then that would give x = +2 and -2

Re: Gmatclub test M 05, question 15/37 [#permalink]

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14 Mar 2010, 23:52

bangalorian2000 wrote:

Also sqrt of positive number is always +ve it can't be negative.

Sqrt of any positive number can be negative, its not necessarily to be positive. for example, if we have 9 as number, than its sqrt can be 3 or -3 since 9 = 3*3 or (-3)*(-3)
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