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# If a=1 and (a-b)/c = 1, which of the following is NOT a

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VP
Joined: 21 Jul 2006
Posts: 1447
If a=1 and (a-b)/c = 1, which of the following is NOT a  [#permalink]

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Updated on: 01 Mar 2012, 00:04
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15% (low)

Question Stats:

77% (00:42) correct 23% (00:53) wrong based on 295 sessions

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If a=1 and (a-b)/c = 1 which of the following is NOT a possible value of b?

A. -2
B. -1
C. 0
D. 1
E. 2

Originally posted by tarek99 on 11 Dec 2007, 03:22.
Last edited by Bunuel on 01 Mar 2012, 00:04, edited 2 times in total.
Edited the question and added the OA
Intern
Joined: 25 Nov 2007
Posts: 38

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11 Dec 2007, 09:08
Answer is D. b cannot be 1.

1-1/c =1 is not possible
Director
Joined: 03 Sep 2006
Posts: 835

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11 Dec 2007, 19:57
1
tarek99 wrote:
If a=1 and (a-b)/c = 1 which of the following is NOT a possible value of b?

A. -2
B. -1
C. 0
D. 1
E. 2

b = (1-c)

If b=1, then C=0, which will not satisfy (a-b)/c = 1. ( divisibility by 0 is not possible.)

therefore b=1 is not possible.
Intern
Joined: 04 Nov 2007
Posts: 49

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11 Dec 2007, 22:32
Since (1-b)/c = 1, b can not be 1. If b = 1, then (1-b)/c will always be 0, violating the rule
Director
Joined: 12 Jul 2007
Posts: 853

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12 Dec 2007, 06:53
1
yezz wrote:
tarek99 wrote:
If a=1 and (a-b)/c = 1, which of the following is NOT a possible value of b?

a) -2

b) -1

c) 0

d) 1

e) 2

all r possible

Equation is:

(a-b)/c = 1 where a = 1

so plug in 1 for a and look at it again

(1-b)/c = 1

now C can be anything we want, so if b = -2 we can plug it in and make it work

(1-(-2))/c = 1
3/c = 1
c = 3 and it works

HOWEVER, if we have a 0 in the numerator there isn't a number on earth that makes 0/C = 1

(1-1)/c = 1
0/c = 1
there aren't any matches for C to make this true

B cannot be 1.

Senior Manager
Joined: 07 Sep 2010
Posts: 288

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29 Feb 2012, 22:51
Hi.
Can anyone let me know what is wrong in my approach -

(a-b)/c = 1

a-b = c(by cross multiplying)
Now as a= 1
1-b = c
implies, 1-c=b
Now c can take any value, and b can have any of the values provided in the answer choices. Please let me know where I am going wrong. Why it is not possible to cross multiply in the first instance. this is how I approached in my exam.

Thanks
Math Expert
Joined: 02 Sep 2009
Posts: 47977

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01 Mar 2012, 00:10
2
imhimanshu wrote:
Hi.
Can anyone let me know what is wrong in my approach -

(a-b)/c = 1

a-b = c(by cross multiplying)
Now as a= 1
1-b = c
implies, 1-c=b
Now c can take any value, and b can have any of the values provided in the answer choices. Please let me know where I am going wrong. Why it is not possible to cross multiply in the first instance. this is how I approached in my exam.

Thanks

If a=1 and (a-b)/c = 1 which of the following is NOT a possible value of b?
A. -2
B. -1
C. 0
D. 1
E. 2

First of all remember that division by zero is undefined, hence $$c\neq{0}$$ and that's why you CAN cross-multiply.

$$\frac{a-b}{c}=1$$ --> as $$a=1$$ --> $$\frac{1-b}{c}=1$$ --> $$1-b=c$$, but since $$c\neq{0}$$, then $$1-b\neq{0}$$ --> $$b\neq{1}$$.

Hope it's clear.
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Posts: 288
Re: If a=1 and (a-b)/c = 1, which of the following is NOT a  [#permalink]

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01 Mar 2012, 00:48
Thanks Bunuel, makes sense. !:-)
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Re: If a=1 and (a-b)/c = 1, which of the following is NOT a  [#permalink]

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11 Nov 2017, 00:30
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Re: If a=1 and (a-b)/c = 1, which of the following is NOT a &nbs [#permalink] 11 Nov 2017, 00:30
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