absolute value

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imane81: Senior | Next Rank: 100 Posts; Posts: 40; Joined: Wed Jan 13, 2010 7:17 pmFollowed by: 1 member; Thanked: 1 times

by imane81 » Tue Feb 16, 2010 1:39 pm

if absolute value(d-9) = 2d, then d=

a. -9
b.-3
c.1
d.3
e.9

The right answer is -9 or 3??
i would go for answer a which is d= -9 but please confirm

would actually like to know if an absolute value should always be taken for its positive value as it is a distance and a distance is always positive

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Source: Beat The GMAT — Problem Solving | Tue Feb 16, 2010 1:39 pm

ajith: Legendary Member; Posts: 1275; Joined: Thu Sep 21, 2006 11:13 pmFollowed by: 2 members; Location: Arabian Sea; Thanked: 125 times

by ajith » Tue Feb 16, 2010 1:51 pm

imane81 wrote:if absolute value(d-9) = 2d, then d=

a. -9
b.-3
c.1
d.3
e.9

The right answer is -9 or 3??
i would go for answer a which is d= -9 but please confirm

would actually like to know if an absolute value should always be taken for its positive value as it is a distance and a distance is always positive

since absolute value always gives a positive value 2d should be positive, so should d

9-d =2d
d=3

or

d-9 =2d
or d= -9 which is not possible since in that case 2d will not be positive

[spoiler]hence d=3[/spoiler]

Always borrow money from a pessimist, he doesn't expect to be paid back.

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money9111: Legendary Member; Posts: 2109; Joined: Sun Apr 19, 2009 10:25 pmFollowed by: 79 members; Location: New Jersey; Thanked: 109 times; GMAT Score:640

by money9111 » Tue Feb 16, 2010 2:44 pm

you got (d-9) because (9-d)*(-1)?

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ajith: Legendary Member; Posts: 1275; Joined: Thu Sep 21, 2006 11:13 pmFollowed by: 2 members; Location: Arabian Sea; Thanked: 125 times

by ajith » Tue Feb 16, 2010 2:48 pm

money9111 wrote:you got (d-9) because (9-d)*(-1)?

absolutely, d-9 can be negative or positive so, we have to consider both

Always borrow money from a pessimist, he doesn't expect to be paid back.

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thephoenix: Legendary Member; Posts: 1560; Joined: Tue Nov 17, 2009 2:38 amFollowed by: 5 members; Thanked: 137 times

by thephoenix » Tue Feb 16, 2010 9:05 pm

ld-9l=2d--------->

+-(d-9)=2d----->

d=+3 or d=-9

now putting values back in eqn=for d=3 we get LHS=RHS

and for d=-9
lHS#RHS

hence d=3

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