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# If n denotes a number to the left of 0 on the number line

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07 Mar 2012, 05:14
can you explain why are you flipping sign?

n> - 1/10.

why 1/n<-10 ?

if n=4 for example 4>-1/10 and 1/4>-10. why to flip sign?
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07 Mar 2012, 06:23
Expert's post
akakhidze wrote:
can you explain why are you flipping sign?

n> - 1/10.

why 1/n<-10 ?

if n=4 for example 4>-1/10 and 1/4>-10. why to flip sign?

Since n denotes a number to the left of 0 on the number then n is negative, so it can not be 4 as you assumed.

Next, when you multiply (or divide) an inequality by a negative number you must flip the sign of the inequality.

So, for $$n>-\frac{1}{10}$$ --> multiply by negative -10 and flip the sign: $$-10n<1$$ --> divide by negative $$n$$ and flip the sign again: $$-10>\frac{1}{n}$$.

For a complete solution refer to the posts above, for example: if-n-denotes-a-number-to-the-left-of-0-on-the-number-line-91659.html#p667838

Hope it helps.
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Re: If n denotes a number to the left of 0 on the number line [#permalink]

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17 Jun 2013, 05:51
Expert's post
Bumping for review and further discussion*. Get a kudos point for an alternative solution!

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Re: If n denotes a number to the left of 0 on the number line [#permalink]

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22 Jun 2013, 07:20
Hi Bunuel
Can it be right if go like the following way?

given (-n)^2<1/100
=>n^2<1/00
=>n<1/10

Now Q ask us to find reciprocal of n
So take the reciprocal on both side simply we get
1/n<10 Ans
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Re: If n denotes a number to the left of 0 on the number line [#permalink]

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07 Nov 2013, 02:03
Expert's post
prasannajeet wrote:
Hi Bunuel
Can it be right if go like the following way?

given (-n)^2<1/100
=>n^2<1/00
=>n<1/10

Now Q ask us to find reciprocal of n
So take the reciprocal on both side simply we get
1/n<10 Ans

No.
Given: n < 0
$$n^2 < (1/100)$$
Note that you will not use -n because n is negative. n already includes the negative sign.
When you take square root, you get |n| < 1/10 (and not n < 1/10). This means -1/10 < n < 1/10. But since n < 0, -1/10 < n < 0.

We need to find the value of reciprocal i.e. 1/n.

n > -1/10
1/n < -10 Note that in an inequality, if both sides of the inequality have the same sign (positive or negative), the sign of inequality (<, >) flips when you take the reciprocal. Here both sides are negative so sign flips.
(Or do what Bunuel did: multiply by -10/n.)
So reciprocal is less than -10.

Instead, I would do this question by thinking of some numbers and figuring out the logic - discussed here: if-n-denotes-a-number-to-the-left-of-0-on-the-number-line-91659.html#p811517
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Re: If n denotes a number to the left of 0 on the number line [#permalink]

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03 Oct 2014, 19:39
Bunuel wrote:
hardnstrong wrote:
i dont get your point bangolarian
we have n^2 < 100 so -1/10 < n < 1/10
how you got n < - 1/10

Can somebody please explain if n > -1/10. does that mean its reciprocal is 1/n < -10 . Do we change less than and greater than sign with reciprocal of any interger?

Refer to my previous post:

We have $$n<0$$ and $$n^2<\frac{1}{100}$$

$$n^2<\frac{1}{100}$$ --> $$-\frac{1}{10}<n<\frac{1}{10}$$, but as $$n<0$$ --> $$-\frac{1}{10}<n<0$$.

Multiply the inequality by $$-\frac{10}{n}$$, (note as $$n<0$$ expression $$-\frac{10}{n}>0$$, and we don't have to switch signs) --> $$(-\frac{1}{10})*(-\frac{10}{n})<n*(-\frac{10}{n})<0*(-\frac{10}{n})$$ --> so finally we'll get $$\frac{1}{n}<-10<0$$. OR $$\frac{1}{n}<-10$$.

Hope it helps.

Hi Bunnel ,

I am weak with inequalities and flipping of signs , where could i get theory for it / additional similar practice questions ?

Thanks and Regards ,
Sheldon Rodrigues
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Re: If n denotes a number to the left of 0 on the number line [#permalink]

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04 Oct 2014, 03:22
Expert's post
shelrod007 wrote:
Bunuel wrote:
hardnstrong wrote:
i dont get your point bangolarian
we have n^2 < 100 so -1/10 < n < 1/10
how you got n < - 1/10

Can somebody please explain if n > -1/10. does that mean its reciprocal is 1/n < -10 . Do we change less than and greater than sign with reciprocal of any interger?

Refer to my previous post:

We have $$n<0$$ and $$n^2<\frac{1}{100}$$

$$n^2<\frac{1}{100}$$ --> $$-\frac{1}{10}<n<\frac{1}{10}$$, but as $$n<0$$ --> $$-\frac{1}{10}<n<0$$.

Multiply the inequality by $$-\frac{10}{n}$$, (note as $$n<0$$ expression $$-\frac{10}{n}>0$$, and we don't have to switch signs) --> $$(-\frac{1}{10})*(-\frac{10}{n})<n*(-\frac{10}{n})<0*(-\frac{10}{n})$$ --> so finally we'll get $$\frac{1}{n}<-10<0$$. OR $$\frac{1}{n}<-10$$.

Hope it helps.

Hi Bunnel ,

I am weak with inequalities and flipping of signs , where could i get theory for it / additional similar practice questions ?

Thanks and Regards ,
Sheldon Rodrigues

Theory on Inequalities
Inequality tips: tips-and-hints-for-specific-quant-topics-with-examples-172096.html#p1379270

inequalities-trick-91482.html
data-suff-inequalities-109078.html
range-for-variable-x-in-a-given-inequality-109468.html
everything-is-less-than-zero-108884.html
graphic-approach-to-problems-with-inequalities-68037.html
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Re: If n denotes a number to the left of 0 on the number line [#permalink]

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06 Oct 2015, 17:57
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Re: If n denotes a number to the left of 0 on the number line [#permalink]

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06 Oct 2015, 19:01
topmbaseeker wrote:
If n denotes a number to the left of 0 on the number line such that the square of n is less than 1/100, then the reciprocal of n must be

A. Less than -10
B. Between -1 and -1/10
C. Between -1/10 and 0
D. Between 0 and 1/10
E. Greater than 10

I will go for A. I find trial and error the best way to solve these questions.
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Re: If n denotes a number to the left of 0 on the number line [#permalink]

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14 Feb 2016, 09:25
These types of problems can be easier to do visually :

Step 1: range of n^2 < 1 /100 | --------- 0 <--------.01 -----|

Step 2: range of \sqrt{n^2} = \sqrt{1/100} (question states only to the left of 0) : | ---------(-1/10)-------->0 ---------|

* note to see if the range of n is going towards 0 or away test a number of n^2 and see what the sq root gives you i.e. \sqrt{1/10000} = +/- \frac{1}{100} which is smaller.

Step 3: inverse of the range n | <--------- (-10) ---- 0 ----------|
Re: If n denotes a number to the left of 0 on the number line   [#permalink] 14 Feb 2016, 09:25

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