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If 0 < x < 1, which of the following inequalities must be [#permalink]
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08 Oct 2008, 06:48
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If 0 < x < 1, which of the following inequalities must be true ? I. \(x^5 < x^3\) II. \(x^4 + x^5 < x^3 + x^2\) III. \(x^4  x^5 < x^2  x^3\) A. None B. I only C. II only D. I and II only E. I, II and III
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Re: If 0 < x < 1, which of the following inequalities must be [#permalink]
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08 Oct 2008, 07:55
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amitdgr wrote: If 0<x<1 , which of the following inequalities must be true ?
I. \(x^5 < x^3\) II. \(x^4 + x^5 < x^3 + x^2\) III. \(x^4  x^5 < x^2  x^3\)
* None * I only * II only * I and II only * I,II and III The answer is E I: x^5x^3 = x^3*(x1)*(x+1) < 0 since x > 0 and x < 1 II: x^4+x^5x^3x^2 = x^2*(x+1)*(x1)*(x+1) < 0 for same reasons III: x^4x^5x^2+x^3 = x^2*(1x)*(x1)*(x+1) = x^2*(x1)^2*(x+1) < 0



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Re: If 0 < x < 1, which of the following inequalities must be [#permalink]
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08 Oct 2008, 08:36
My two cents: I beeter if you divided by x^2: x^2+x^3<x+1 > always II better if you divided by x^2: x^2x^3<1x^2 always III dividing by x^2: x^2x^3<1x^2 if x=0.1 thus 0.010.001<10.01 always if x=0.9 thus 0.810.729<10.9 // 0.081<1 always EOA? Cheers
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Re: If 0 < x < 1, which of the following inequalities must be [#permalink]
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08 Oct 2008, 09:01
I also believe the answer is E since even the third equation, x^4  x^5 < x^2  x^3 = x^4 + x^3 < x^2 + x^5 =x^2 + x < 1+x^3 which is true since the value on the right hand side will be greater than 1.
thanks SM



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Re: If 0 < x < 1, which of the following inequalities must be [#permalink]
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08 Oct 2008, 10:33
i will also go with E
raising a decimal number to any power reduces the value of the number. so .1^2=.01 and .1^3=.001
can be solved by picking numbers



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If 0 < x < 1, which of the following inequalities must be [#permalink]
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Re: If 0 < x < 1, which of the following inequalities must be [#permalink]
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28 May 2015, 22:43
Bunuel wrote: scofield1521 wrote: People, please throw some more light!! If 0 < x < 1, which of the following inequalities must be true ?I. \(x^5 < x^3\) II. \(x^4 + x^5 < x^3 + x^2\) III. \(x^4  x^5 < x^2  x^3\) A. None B. I only C. II only D. I and II only E. I, II and III If 0 < x < 1, then x > x^2 > x^3 > x^4 > x^5 ... I. \(x^5 < x^3\). True. II. \(x^4 + x^5 < x^3 + x^2\). Each term on the left hand side is less than each term on the right hand side, thus LHS < RHS. III. \(x^4  x^5 < x^2  x^3\) > \(x^4(1  x) < x^2(1  x)\). Since 0 < x < 1, then 1  x > 0, so we can reduce by it: \(x^4 < x^2\). True. Answer: E. Hope it's clear. Bunuel Can we do this question algebraically without substituting fractions? By trying to prove that each of the statements given indeed have x values within the range of 0 and 1 on the number line?



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Re: If 0 < x < 1, which of the following inequalities must be [#permalink]
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28 May 2015, 23:35
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sinhap07 wrote: Bunuel wrote: scofield1521 wrote: People, please throw some more light!! If 0 < x < 1, which of the following inequalities must be true ?I. \(x^5 < x^3\) II. \(x^4 + x^5 < x^3 + x^2\) III. \(x^4  x^5 < x^2  x^3\) A. None B. I only C. II only D. I and II only E. I, II and III If 0 < x < 1, then x > x^2 > x^3 > x^4 > x^5 ... I. \(x^5 < x^3\). True. II. \(x^4 + x^5 < x^3 + x^2\). Each term on the left hand side is less than each term on the right hand side, thus LHS < RHS. III. \(x^4  x^5 < x^2  x^3\) > \(x^4(1  x) < x^2(1  x)\). Since 0 < x < 1, then 1  x > 0, so we can reduce by it: \(x^4 < x^2\). True. Answer: E. Hope it's clear. Bunuel Can we do this question algebraically without substituting fractions? By trying to prove that each of the statements given indeed have x values within the range of 0 and 1 on the number line? Hi sinhap07, Please find the algebraic approach for the question I. \(x^5 <x^3\)\(x^3(x^2  1) < 0\) i.e. \(x^3 (x 1) (x +1) < 0.\) Using the wavy line method we know that for \(0 < x < 1\) the inequality holds true.II.\(x^4 + x^5 < x^3 + x^2\)\(x^5  x^3 + x^4  x^2 < 0\) i.e. \(x^2(x 1) (x + 1)^2 < 0\) Using wavy line method we know that for \(0 < x < 1\) the inequality holds trueIII.\(x^4  x^5 < x^2  x^3\)\(x^4  x^2  x^5 + x^3 < 0\) i.e. \(x^2 (x + 1)(x  1) (1 x) < 0\) \(x^2 (x 1)^2(x + 1) > 0\) Using wavy line method we know that for \(0 < x < 1\) the inequality holds true Thus all the three inequalities are true for the range \(0 < x < 1\) Hope it's clear Regards Harsh
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Re: If 0 < x < 1, which of the following inequalities must be [#permalink]
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28 May 2015, 23:52
Bunuel Can we do this question algebraically without substituting fractions? By trying to prove that each of the statements given indeed have x values within the range of 0 and 1 on the number line?[/quote] Hi sinhap07, Please find the algebraic approach for the question I. \(x^5 <x^3\)\(x^3(x^2  1) < 0\) i.e. \(x^3 (x 1) (x +1) < 0.\) Using the wavy line method we know that for \(0 < x < 1\) the inequality holds true.II.\(x^4 + x^5 < x^3 + x^2\)\(x^5  x^3 + x^4  x^2 < 0\) i.e. \(x^2(x 1) (x + 1)^2 < 0\) Using wavy line method we know that for \(0 < x < 1\) the inequality holds trueIII.\(x^4  x^5 < x^2  x^3\)\(x^4  x^2  x^5 + x^3 < 0\) i.e. \(x^2 (x + 1)(x  1) (1 x) < 0\) \(x^2 (x 1)^2(x + 1) > 0\) Using wavy line method we know that for \(0 < x < 1\) the inequality holds true Thus all the three inequalities are true for the range \(0 < x < 1\) Hope it's clear Regards Harsh[/quote] Thanks Harsh for your reply. Can you please throw some more light on the wave method? Of what I knw, signs usually alternate but what I see in your workings, signs don't always alternate. Can you explain it? Second, why are we ignoring the negative portions say in statement 1 that makes it less than 1. It shows x values dont only pertain to 0 and 1 region. So how can stmt 1 be sufficient?



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Re: If 0 < x < 1, which of the following inequalities must be [#permalink]
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29 May 2015, 00:32
Quote: Bunuel
Can we do this question algebraically without substituting fractions? By trying to prove that each of the statements given indeed have x values within the range of 0 and 1 on the number line? Quote: Hi sinhap07, Please find the algebraic approach for the question I. \(x^5 <x^3\)\(x^3(x^2  1) < 0\) i.e. \(x^3 (x 1) (x +1) < 0.\) Using the wavy line method we know that for \(0 < x < 1\) the inequality holds true.II.\(x^4 + x^5 < x^3 + x^2\)\(x^5  x^3 + x^4  x^2 < 0\) i.e. \(x^2(x 1) (x + 1)^2 < 0\) Using wavy line method we know that for \(0 < x < 1\) the inequality holds trueIII.\(x^4  x^5 < x^2  x^3\)\(x^4  x^2  x^5 + x^3 < 0\) i.e. \(x^2 (x + 1)(x  1) (1 x) < 0\) \(x^2 (x 1)^2(x + 1) > 0\) Using wavy line method we know that for \(0 < x < 1\) the inequality holds true Thus all the three inequalities are true for the range \(0 < x < 1\) Hope it's clear Regards Harsh Quote: Thanks Harsh for your reply. Can you please throw some more light on the wave method? Of what I knw, signs usually alternate but what I see in your workings, signs don't always alternate. Can you explain it? Second, why are we ignoring the negative portions say in statement 1 that makes it less than 1. It shows x values dont only pertain to 0 and 1 region. So how can stmt 1 be sufficient? Hi sinhap07, You are right when you say signs usually alternate around zero points of the inequality but they only alternate when the expression is sign dependent i.e. for odd powers. For example sign of \(x^3\) is dependent on the sign of \(x\) but sign of \(x^2\) is independent of sign of \(x\). Hence for expressions, signs of which are independent of the signs of their base variable, the wave would not alternate but rather bounce back to the same region it is currently in. I would also suggest you to go through this post on Wavy Line method which will help you understand it better. For your second query, in stI the range of \(x\) for which the inequality holds is \(0 < x < 1\) or \(x < 1\) as seen from the wavy line diagram. However as the question asks us if the inequality is true for the range \(0 < x < 1\), we are not concerned about the other possible values of x for which the inequality is true. Once the inequality satisfies the range \(0 < x < 1\), we have our answer. Hope it's clear Regards Harsh
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Re: If 0 < x < 1, which of the following inequalities must be [#permalink]
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29 May 2015, 22:58
EgmatQuantExpert wrote: Quote: Bunuel
Can we do this question algebraically without substituting fractions? By trying to prove that each of the statements given indeed have x values within the range of 0 and 1 on the number line? Quote: Hi sinhap07, Please find the algebraic approach for the question I. \(x^5 <x^3\)\(x^3(x^2  1) < 0\) i.e. \(x^3 (x 1) (x +1) < 0.\) Using the wavy line method we know that for \(0 < x < 1\) the inequality holds true.II.\(x^4 + x^5 < x^3 + x^2\)\(x^5  x^3 + x^4  x^2 < 0\) i.e. \(x^2(x 1) (x + 1)^2 < 0\) Using wavy line method we know that for \(0 < x < 1\) the inequality holds trueIII.\(x^4  x^5 < x^2  x^3\)\(x^4  x^2  x^5 + x^3 < 0\) i.e. \(x^2 (x + 1)(x  1) (1 x) < 0\) \(x^2 (x 1)^2(x + 1) > 0\) Using wavy line method we know that for \(0 < x < 1\) the inequality holds true Thus all the three inequalities are true for the range \(0 < x < 1\) Hope it's clear Regards Harsh Quote: Thanks Harsh for your reply. Can you please throw some more light on the wave method? Of what I knw, signs usually alternate but what I see in your workings, signs don't always alternate. Can you explain it? Second, why are we ignoring the negative portions say in statement 1 that makes it less than 1. It shows x values dont only pertain to 0 and 1 region. So how can stmt 1 be sufficient? Hi sinhap07, You are right when you say signs usually alternate around zero points of the inequality but they only alternate when the expression is sign dependent i.e. for odd powers. For example sign of \(x^3\) is dependent on the sign of \(x\) but sign of \(x^2\) is independent of sign of \(x\). Hence for expressions, signs of which are independent of the signs of their base variable, the wave would not alternate but rather bounce back to the same region it is currently in. I would also suggest you to go through this post on Wavy Line method which will help you understand it better. For your second query, in stI the range of \(x\) for which the inequality holds is \(0 < x < 1\) or \(x < 1\) as seen from the wavy line diagram. However as the question asks us if the inequality is true for the range \(0 < x < 1\), we are not concerned about the other possible values of x for which the inequality is true. Once the inequality satisfies the range \(0 < x < 1\), we have our answer. Hope it's clear Regards Harsh Ok Harsh, but by the same logic haven't been able to crack the question below? Can you help? If –1 < x < 1 and x ≠ 0, which of the following inequalities must be true? I. x3 < x II. x2 < x III. x4 – x5 > x3 – x2 (A) I only (B) II only (C) III only (D) II and III only (E) I, II, and III



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Re: If 0 < x < 1, which of the following inequalities must be [#permalink]
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30 May 2015, 10:28
sinhap07 wrote: EgmatQuantExpert wrote: Quote: Bunuel
Can we do this question algebraically without substituting fractions? By trying to prove that each of the statements given indeed have x values within the range of 0 and 1 on the number line? Quote: Hi sinhap07, Please find the algebraic approach for the question I. \(x^5 <x^3\)\(x^3(x^2  1) < 0\) i.e. \(x^3 (x 1) (x +1) < 0.\) Using the wavy line method we know that for \(0 < x < 1\) the inequality holds true.II.\(x^4 + x^5 < x^3 + x^2\)\(x^5  x^3 + x^4  x^2 < 0\) i.e. \(x^2(x 1) (x + 1)^2 < 0\) Using wavy line method we know that for \(0 < x < 1\) the inequality holds trueIII.\(x^4  x^5 < x^2  x^3\)\(x^4  x^2  x^5 + x^3 < 0\) i.e. \(x^2 (x + 1)(x  1) (1 x) < 0\) \(x^2 (x 1)^2(x + 1) > 0\) Using wavy line method we know that for \(0 < x < 1\) the inequality holds true Thus all the three inequalities are true for the range \(0 < x < 1\) Hope it's clear Regards Harsh Quote: Thanks Harsh for your reply. Can you please throw some more light on the wave method? Of what I knw, signs usually alternate but what I see in your workings, signs don't always alternate. Can you explain it? Second, why are we ignoring the negative portions say in statement 1 that makes it less than 1. It shows x values dont only pertain to 0 and 1 region. So how can stmt 1 be sufficient? Hi sinhap07, You are right when you say signs usually alternate around zero points of the inequality but they only alternate when the expression is sign dependent i.e. for odd powers. For example sign of \(x^3\) is dependent on the sign of \(x\) but sign of \(x^2\) is independent of sign of \(x\). Hence for expressions, signs of which are independent of the signs of their base variable, the wave would not alternate but rather bounce back to the same region it is currently in. I would also suggest you to go through this post on Wavy Line method which will help you understand it better. For your second query, in stI the range of \(x\) for which the inequality holds is \(0 < x < 1\) or \(x < 1\) as seen from the wavy line diagram. However as the question asks us if the inequality is true for the range \(0 < x < 1\), we are not concerned about the other possible values of x for which the inequality is true. Once the inequality satisfies the range \(0 < x < 1\), we have our answer. Hope it's clear Regards Harsh Ok Harsh, but by the same logic haven't been able to crack the question below? Can you help? If –1 < x < 1 and x ≠ 0, which of the following inequalities must be true? I. x3 < x II. x2 < x III. x4 – x5 > x3 – x2 (A) I only (B) II only (C) III only (D) II and III only (E) I, II, and III Hi sinhap07, Please refer to this post where Japinder has presented the algebraic approach using the wavy line method. Request you to go through it and let us know if you have trouble at any point of the solution Regards Harsh
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Re: If 0 < x < 1, which of the following inequalities must be [#permalink]
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01 Jun 2015, 08:25
Ok Harsh, but by the same logic haven't been able to crack the question below? Can you help? If –1 < x < 1 and x ≠ 0, which of the following inequalities must be true? I. x3 < x II. x2 < x III. x4 – x5 > x3 – x2 (A) I only (B) II only (C) III only (D) II and III only (E) I, II, and III[/quote] Hi sinhap07, Please refer to this post where Japinder has presented the algebraic approach using the wavy line method. Request you to go through it and let us know if you have trouble at any point of the solution Regards Harsh[/quote] Hey Harsh Saw Japinder's solution and posted some concerns. Haven't managed a reply yet. Pls find below my comments. Japinder two concerns: 1. why have we not flipped the inequality sign for stmt 2 when changing the sign to negative? 2. for stmt 3, we have x values less than 1 till negative infinity. how can this be sufficient as the range we want it to be is from 1 to +1



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Re: If 0 < x < 1, which of the following inequalities must be [#permalink]
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01 Jun 2015, 22:53
Quote: sinhap07 wrote: Ok Harsh, but by the same logic haven't been able to crack the question below? Can you help?
If –1 < x < 1 and x ≠ 0, which of the following inequalities must be true? I. x3 < x II. x2 < x III. x4 – x5 > x3 – x2 (A) I only (B) II only (C) III only (D) II and III only (E) I, II, and III Hi sinhap07, Please refer to this post where Japinder has presented the algebraic approach using the wavy line method. Request you to go through it and let us know if you have trouble at any point of the solution Regards Harsh Hey Harsh Saw Japinder's solution and posted some concerns. Haven't managed a reply yet. Pls find below my comments. Japinder two concerns: 1. why have we not flipped the inequality sign for stmt 2 when changing the sign to negative? 2. for stmt 3, we have x values less than 1 till negative infinity. how can this be sufficient as the range we want it to be is from 1 to +1 Hi sinhap07Please refer to the post here where Japinder has addressed your concerns. Also restraint from posting doubts of a question into another question's thread for avoiding confusion to others. Hope this helps Regards Harsh
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Re: If 0 < x < 1, which of the following inequalities must be [#permalink]
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23 Jan 2016, 09:41
amitdgr wrote: If 0 < x < 1, which of the following inequalities must be true ?
I. \(x^5 < x^3\) II. \(x^4 + x^5 < x^3 + x^2\) III. \(x^4  x^5 < x^2  x^3\)
A. None B. I only C. II only D. I and II only E. I, II and III I've started with I: just pick x=1/2 > 1/32<1/8. Now look at the answer choices which would be easier to test. As we already know "I" is correct, now, if we test III and it's correct, we don't need to test II anymore, because the only answer choice that has I and III is E. If you manipulate III as stated in many solutions here, one can see that it must be true > Answer E (we could save some time by picking III after I)
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Re: If 0 < x < 1, which of the following inequalities must be [#permalink]
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amitdgr wrote: If 0 < x < 1, which of the following inequalities must be true ?
I. \(x^5 < x^3\) II. \(x^4 + x^5 < x^3 + x^2\) III. \(x^4  x^5 < x^2  x^3\)
A. None B. I only C. II only D. I and II only E. I, II and III There is a clear indication that x is a positive decimal (fraction) Let us say 0.5 When a positive decimal is squared it becomes smaller than the original value 0.5>0.25 Every subsequent increase in exponent makes a decimal smaller than the earlier one 0.5>0.25>0.125 I. \(x^5 < x^3\) TRUE II. \(x^4 + x^5 < x^3 + x^2\) \(x^4(x+1) < x^2(x+1)\) cancel (x+1 from both side) \(x^4< x^2\) TRUE III. \(x^4  x^5 < x^2  x^3\) \(x^4(1x) < x^2(1x)\) (cancel (1x) from both side \(x^4 < x^2\) TRUE ANSWER IS E (I,II, and II)
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Re: If 0 < x < 1, which of the following inequalities must be [#permalink]
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09 Sep 2016, 09:04
first teo are obvious.... for 3rd....it is logical that...difference between X^4X5 will be less than X^2X^3.



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If 0 < x < 1, which of the following inequalities must be [#permalink]
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18 Nov 2017, 18:37
amitdgr wrote: If 0 < x < 1, which of the following inequalities must be true ?
I. \(x^5 < x^3\) II. \(x^4 + x^5 < x^3 + x^2\) III. \(x^4  x^5 < x^2  x^3\)
A. None B. I only C. II only D. I and II only E. I, II and III When you get handed a gift . . . I looked at the answer choices and decided to test option III, which is included only in Answer E. If option III must be true, the answer is E. (And if III is not part of the answer, given the answer choices, I would be in no worse shape than if I had started with option I.) Let x = \(\frac{1}{2}\) III. \(x^4  x^5 < x^2  x^3\) \(\frac{1}{16}  \frac{1}{32} < \frac{1}{4}  \frac{1}{8}\) ?? LHS: \(\frac{2}{32}  \frac{1}{32} = \frac{1}{32}\) RHS: \(\frac{2}{8}  \frac{1}{8} = \frac{1}{8}\) \(\frac{1}{32} < \frac{1}{8}\) TRUE ANSWER E
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