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Bill is 88 years old. How old is Colie?

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Bill is 88 years old. How old is Colie?  [#permalink]

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New post 04 Oct 2015, 03:55
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A
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C
D
E

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Question Stats:

91% (01:00) correct 9% (00:53) wrong based on 53 sessions

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Bill is 88 years old. How old is Colie?

(1) 4 years ago Colie was twice as old as Dino will be in 2 years.

(2) Bill is twice as old as Colie and Dino combined.

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Bill is 88 years old. How old is Colie?  [#permalink]

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New post Updated on: 04 Oct 2015, 12:53
Gnpth wrote:
Bill is 88 years old. How old is Colie?

(1) 4 years ago Colie was twice as old as Dino will be in 2 years.

(2) Bill is twice as old as Colie and Dino combined.


B=88, C=?

Per statement 1, (C-4) = 2(D+2) ---> C-2D=8 , no information on D. Not sufficient.

Per statement 2, B=2(C+D) ---> From the given condition that B=88 ---> 2(C+D)=88---> C+D = 44 , no information on D or C. Not sufficient.

Combining, you get 2 distinct equations in 2 variables (C-2D=8 and C+D=44) and thus you will get a unique answer for age of Collie (=C). Thus C is the correct answer.

Originally posted by ENGRTOMBA2018 on 04 Oct 2015, 04:25.
Last edited by ENGRTOMBA2018 on 04 Oct 2015, 12:53, edited 1 time in total.
Updated the solution to be clearer.
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Re: Bill is 88 years old. How old is Colie?  [#permalink]

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New post 04 Oct 2015, 12:19
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Engr2012 wrote:
Gnpth wrote:
Bill is 88 years old. How old is Colie?

(1) 4 years ago Colie was twice as old as Dino will be in 2 years.

(2) Bill is twice as old as Colie and Dino combined.


B=88, C=?

Per statement 1, (C-4) = 2(D+2) ---> C-2D=8 , no information on D. Not sufficient.

Per statement 2, B=2(C+D) ---> C+D=44 , no information on D or C. Not sufficeint.

Combining, you get 2 distinct equations in 2 variables and thus you will get a unique answer for age of Collie. Thus C is the correct answer.


Hi Engr2012,

While I agree with the correct answer, and how you dealt with each of the two individual Facts, the explanation that you've offered for the correct answer isn't explicitly correct (for the reason that you described). When combining the two Facts, you end up with 3 variables and 2 equations - when combined with the original equation that appears in the prompt (B = 88), then you have 3 variables with 3 unique equations, which you CAN solve.

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Bill is 88 years old. How old is Colie?  [#permalink]

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New post 04 Oct 2015, 12:48
EMPOWERgmatRichC wrote:
Engr2012 wrote:
Gnpth wrote:
Bill is 88 years old. How old is Colie?

(1) 4 years ago Colie was twice as old as Dino will be in 2 years.

(2) Bill is twice as old as Colie and Dino combined.


B=88, C=?

Per statement 1, (C-4) = 2(D+2) ---> C-2D=8 , no information on D. Not sufficient.

Per statement 2, B=2(C+D) ---> C+D=44 , no information on D or C. Not sufficeint.

Combining, you get 2 distinct equations in 2 variables and thus you will get a unique answer for age of Collie. Thus C is the correct answer.


Hi Engr2012,

While I agree with the correct answer, and how you dealt with each of the two individual Facts, the explanation that you've offered for the correct answer isn't explicitly correct (for the reason that you described). When combining the two Facts, you end up with 3 variables and 2 equations - when combined with the original equation that appears in the prompt (B = 88), then you have 3 variables with 3 unique equations, which you CAN solve.

GMAT assassins aren't born, they're made,
Rich


EMPOWERgmatRichC, thank you for your observation. You are absolutely correct. I forgot to mention the equation B=44 and this equation along with the 2 other equations in C and D, would have provided you with 3 distinct equations and 3 variables.

I did the equations mentally and thus missed this subtle aspect of the explanation. I have updated my solution in light of this observation.
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Re: Bill is 88 years old. How old is Colie?  [#permalink]

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New post 27 Mar 2019, 09:54
As per Kaplan, this is the explanation (see below). I found this to be a helpful response. The trick here is to use one to plug into the other.
-----
The correct answer is C

We want to determine the age of Colie. We are told that Bill is 88 years old. Since no other information in given in the question stem, let's look at the statements.

Let's call Colie's age c and Dino's age d. Statement (1) says that c - 4 = 2(d + 2). This equation can be rewritten c - 4 = 2d + 4, and then c = 2d + 8. This is a single linear equation with two variables. This equation cannot be solved for the value of either variable. So the value of c cannot be solved for. Statement (1) is insufficient and choices (A) and (D) can be eliminated.

Statement (2) says that 88 = 2(c + d). This is a single linear equation with two variables. This equation cannot be solved for the value of either variable. So the value of c cannot be solved for. Statement (2) is insufficient as well and choice (B) can be eliminated.

Taking the statements together we have the equations c = 2d + 8 and 88 = 2(c + d). We have two different linear equations in the variables c and d. These two equations can be solved for the values of each variable. Thus, c has a single value that can be solved for. The two statements taken together are sufficient and choice (C) is correct.
-----

Gnpth wrote:
Bill is 88 years old. How old is Colie?

(1) 4 years ago Colie was twice as old as Dino will be in 2 years.

(2) Bill is twice as old as Colie and Dino combined.
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Re: Bill is 88 years old. How old is Colie?   [#permalink] 27 Mar 2019, 09:54
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