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Bunuel
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ARYAKASHANDILYA

Bunuel
Official Solution:


If \(m \neq 0\) and \(\frac{m^4}{|m|} < \sqrt{m^2}\), then which of the following must be true?

I. \(m < \pi\)

II. \(m^2 < 1\)

III. \(m^3 > -8\)


A. I only
B. II only
C. III only
D. I and II only
E. I, II, and III


Since \(\sqrt{m^2} = |m|\), we have \(\frac{m^4}{|m|} < |m|\).

Multiplying both sides by \(|m|\), we get \(m^4 < m^2\).

Dividing both sides by \(m^2\), we have \(m^2 < 1\).

This inequality implies that \(-1 < m < 1\).

So, essentially, the question asks: Given that \(-1 < m < 1\), which of the following statements must be true?

I. \(m < \pi\). Since \(-1 < m < 1\), it is correct to say that for any \(m\) from this range, \(m < \pi\).

II. \(m^2 < 1\). This statement is already established to be true from our earlier steps. So, this statement is always true.

III. \(m^3 > -8\). This inequality implies that \(m > -2\). Since \(-1 < m < 1\), it is true for all values of \(m\) in this range that \(m > -2\).


Answer: E


Bunuel Thanks for the explanation.
However , since its a must be true question, Incase of X<pie, how will x satisfy for -3 and -2
Similarly for option 3, x will not satisfy.

Can you please explain?

We got that \(-1 < m < 1\), so m cannot be -3 or -2.

This question belongs to a type of question that tends to be very confusing for many. Therefore, I recommend practicing similar questions from the following collection: Trickiest Inequality Questions Type: Confusing Ranges.
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I did not quite understand the solution. I understood II but, m's value had this range -1<m<1, then how m<pi or m^3>-8 justifies this?
Bunuel ?
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I did not quite understand the solution. I understood II but, m's value had this range -1<m<1, then how m<pi or m^3>-8 justifies this?
Bunuel ?

We have that \(-1 < m < 1\).

Any m from this range will be less than \(\pi\), which is approximately 3.14, and any m from that range when cubed will be more than -8.

This question belongs to a type of question that tends to be very confusing for many. Therefore, I recommend practicing similar questions from the following collection: Trickiest Inequality Questions Type: Confusing Ranges.
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I did not quite understand the solution. Bunuel can the wavy curve method be used for this question? I tried using it and didn't get the correct answer. If it can't be used any chance you could please explain why?
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sb995
I did not quite understand the solution. Bunuel can the wavy curve method be used for this question? I tried using it and didn't get the correct answer. If it can't be used any chance you could please explain why?

You can check alternative solutions here: https://gmatclub.com/forum/gmat-club-wo ... 95426.html (that thread includes the method you mentioned). Let me know if you still have any questions.

P.S. This question belongs to a type of question that tends to be very confusing for many. Therefore, I recommend practicing similar questions from the following collection: Trickiest Inequality Questions Type: Confusing Ranges.
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Bunuel

I have the following question:

How is Multiplying both sides of m^4 / |m|<|m| by |m| results in m^4<m^2 ?

Isn't |m| *|m| = |m| ^2 instead of m^2?

Aren't |m|^2 and m^2 different from each other?

btw, we only know dat m is non-zero, but we donot know anything about it's sign.


Thanks in Advance!
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Rebaz
Bunuel

I have the following question:

How is Multiplying both sides of m^4 / |m|<|m| by |m| results in m^4<m^2 ?

Isn't |m| *|m| = |m| ^2 instead of m^2?

Aren't |m|^2 and m^2 different from each other?

btw, we only know dat m is non-zero, but we donot know anything about it's sign.


Thanks in Advance!

1. No. |m|^2 = m^2. Squaring takes care of the modulus.
2. |m| is always non-negative and since given that m is not 0, then in this case it's positive only.
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