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Re: Is r^x < 100? [#permalink]
Bunuel wrote:
Is \(r^x < 100\)?


(1) \(r*\sqrt[3]{x}>100\)

(2) \(x> 1\)


Statement 1: if \(r<0\), then \(x<0\) and if \(r>0\) then \(x>0\)

\(r=-200\) & \(x=-8\), then \(r*\sqrt[3]{x}\) \(=-200*-2=400>100\)

but \(r^x\) \(= (-200)^{-8} = \frac{1}{(-200)^8}\)\(<100\)

if \(r=200\) and \(x=8\), then \(r*\sqrt[3]{x}>100\) \(=200*2=400>100\)

but \(r^x=200^8>100\). Hence insufficient

Statement 2: \(x>\)1 but nothing given about \(r\). hence insufficient

Combining 1 & 2 if \(r=200\) and \(x=8\), then \(r*\sqrt[3]{x}>100\) \(=200*2=400>100\), then the answer to our question Stem is NO.

but if \(x=0.5\) and \(r=10^9\), then \(r*\sqrt[3]{x}>100\) \(=0.5*10^3=500>100\) but \(r^x=(0.5)^{10^9}<100\). So we get a Yes for our question stem.

Hence Insufficient

Option E

Originally posted by niks18 on 03 Oct 2017, 03:50.
Last edited by niks18 on 04 Oct 2017, 07:39, edited 1 time in total.
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Re: Is r^x < 100? [#permalink]
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Kudos
niks18 wrote:
Bunuel wrote:
Is \(r^x < 100\)?


(1) \(r*\sqrt[3]{x}>100\)

(2) \(x> 1\)


Statement 1: if \(r<0\), then \(x<0\) and if \(r>0\) then \(x>0\)

\(r=-200\) & \(x=-8\), then \(r*\sqrt[3]{x}\) \(=-200*-2=400>100\)

but \(r^x\) \(= (-200)^{-8} = \frac{1}{(-200)^8}\)\(<100\)

if \(r=200\) and \(x=8\), then \(r*\sqrt[3]{x}>100\) \(=200*2=400>100\)

but \(r^x=200^8>100\). Hence insufficient

Statement 2: \(x>\)1 but nothing given about \(r\). hence insufficient

Combining 1 & 2 we know that \(x>0\), hence \(r>0\) so \(r^x>100\). Hence we get a NO for our question stem. Sufficient

Option C


Hi niks18,

When you combine 1 & 2

beside your example, you neglected when x is huge number and 0<r<1

if \(r=200\) and \(x=8\), then \(r*\sqrt[3]{x}>100\) \(=200*2=400>100\).......Is 200^8 < 100........Answer No

if \(r=0.2\) and \(x=10^9\), then \(r*\sqrt[3]{x}>100\) \(=0.2 *1000=200>100\).....Is (0.2)^1000000000 < 100...Answer Yes

It should be E
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Re: Is r^x < 100? [#permalink]
Mo2men wrote:
niks18 wrote:
Bunuel wrote:
Is \(r^x < 100\)?


(1) \(r*\sqrt[3]{x}>100\)

(2) \(x> 1\)


Statement 1: if \(r<0\), then \(x<0\) and if \(r>0\) then \(x>0\)

\(r=-200\) & \(x=-8\), then \(r*\sqrt[3]{x}\) \(=-200*-2=400>100\)

but \(r^x\) \(= (-200)^{-8} = \frac{1}{(-200)^8}\)\(<100\)

if \(r=200\) and \(x=8\), then \(r*\sqrt[3]{x}>100\) \(=200*2=400>100\)

but \(r^x=200^8>100\). Hence insufficient

Statement 2: \(x>\)1 but nothing given about \(r\). hence insufficient

Combining 1 & 2 we know that \(x>0\), hence \(r>0\) so \(r^x>100\). Hence we get a NO for our question stem. Sufficient

Option C


Hi niks18,

When you combine 1 & 2

beside your example, you neglected when x is huge number and 0<r<1

if \(r=200\) and \(x=8\), then \(r*\sqrt[3]{x}>100\) \(=200*2=400>100\).......Is 200^8 < 100........Answer No

if \(r=0.2\) and \(x=10^9\), then \(r*\sqrt[3]{x}>100\) \(=0.2 *1000=200>100\).....Is (0.2)^1000000000 < 100...Answer Yes

It should be E


Hi Mo2men

Yup agreed :thumbup: . Thanks for highlighting, will edit the solution
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Re: Is r^x < 100? [#permalink]
Bunuel wrote:
Is \(r^x < 100\)?


(1) \(r*\sqrt[3]{x}>100\)

(2) \(x> 1\)



Hello Bunuel, i am getting answer : E ( have shared the solution above)

is OA=C correct ? if so can you please share the solution and also please let me know what mistake i made ?

Thanks
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Re: Is r^x < 100? [#permalink]
Expert Reply
Bunuel wrote:
Is \(r^x < 100\)?


(1) \(r*\sqrt[3]{x}>100\)

(2) \(x> 1\)



hi Bunuel...
OA should be E.

combined if r>1, most of the time \(r^x>100\)
if 0<r<1, \(r^x<100\) always
so insuff

E
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Re: Is r^x < 100? [#permalink]
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Re: Is r^x < 100? [#permalink]
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