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# Is the slope of the line l equal to -1/5?

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Math Expert
Joined: 02 Sep 2009
Posts: 54696
Is the slope of the line l equal to -1/5?  [#permalink]

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25 Jul 2017, 03:59
1
3
00:00

Difficulty:

65% (hard)

Question Stats:

51% (01:29) correct 49% (01:11) wrong based on 85 sessions

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Is the slope of the line l equal to -1/5?

(1) Lines m and n are parallel and sum of their slopes is less than 1/2.
(2) Line l is perpendicular to line m.

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Joined: 29 May 2017
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Is the slope of the line l equal to -1/5?  [#permalink]

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25 Jul 2017, 04:58
3
1. The slope of line m and n has to be less than 1/4. Not sufficient.

2. If l and m are perpendicular, the product of their slope should be equal to -1 and for the slope of l to be -1/5 , the slope of m should be equal to 5 but no info on that. Not sufficient.

However, taking 1 and 2 combined, we are certain that slope of m can never be 5 so the slope of l can never be -1/5.

Hence, I go with C.

Kudos, if agree.
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Re: Is the slope of the line l equal to -1/5?  [#permalink]

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25 Jul 2017, 22:22
Bunuel wrote:
Is the slope of the line l equal to -1/5?

(1) Lines m and n are parallel and sum of their slopes is less than 1/2.
(2) Line l is perpendicular to line m.

(1) Let slope be m and n for respective lines
$$m=n$$
$$m+m<1/2$$
$$m<1/4$$
not sufficient

(2) $$l*m = -1$$
not sufficient

on combining
$$m=-1/l$$
$$-1/l<1/4$$
$$1/l>1/4$$
$$0<l<4$$
Sufficient

Hence C
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Luckisnoexcuse
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Re: Is the slope of the line l equal to -1/5?  [#permalink]

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29 Aug 2017, 01:14
Luckisnoexcuse wrote:
Bunuel wrote:
Is the slope of the line l equal to -1/5?

(1) Lines m and n are parallel and sum of their slopes is less than 1/2.
(2) Line l is perpendicular to line m.

(1) Let slope be m and n for respective lines
$$m=n$$
$$m+m<1/2$$
$$m<1/4$$
not sufficient

(2) $$l*m = -1$$
not sufficient

on combining
$$m=-1/l$$
$$-1/l<1/4$$
$$1/l>1/4$$
$$0<l<4$$
Sufficient

Hence C

can u elaborate how come

−1/l<1/4
1/l>1/4

i think 1/L > -1/4
if u are multiplying with -ve on both sides

??
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Re: Is the slope of the line l equal to -1/5?  [#permalink]

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29 Aug 2017, 01:22
Ans is C:

1) insufficient as does not tell us about slope of l
2) insufficient no info about m

combining both

m= -1/L
and also m+m < 1/2
m<1/4

ie -1/L < 1/4
therefore L can take values (-infinity, -4) U (0, + infinity)

Clearly L can not take value from -4 to 0 therefore the slope can never be -1/5
Definite NO

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Re: Is the slope of the line l equal to -1/5?   [#permalink] 29 Aug 2017, 01:22
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