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GMAT 2nd edition (little green book) Age question

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GMAT 2nd edition (little green book) Age question

by hutch27 » Wed Apr 10, 2013 11:13 am
Today rose is twice as old as Sam and Sam is 3 years younger than Tina. If Rose, Same, and Tima are all alive 4 years from today, which of the following must be true on that day.

1- Rose is twice as old as sam
2- sam is 3 years younger than tina
3- rose is older than tina

A: I only
B: II only
C: III only
D: I and II
E: II and III

OA is B

My question is, how does one go about solving age questions on the GMAT? I tried using an approach Brent suggested but it led me to get the wrong answer :cry: Would picking numbers be the fastest way to solve these types of word problems?
Last edited by hutch27 on Wed Apr 10, 2013 1:32 pm, edited 1 time in total.
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by Anju@Gurome » Wed Apr 10, 2013 11:22 am
hutch27 wrote:Today rose is twice as old as Sam and Sam is 3 years younger than Tina. If Rose, Same, and Tima are all alive 4 years from today, which of the following must be true on that day.

1- Rose is twice as old as sam
2- sam is 3 years younger than tina
3- rose is older than tina
Let us assume that today their ages are R, S, and T.
So, R = 2S and S = T - 3

After 4 years, their ages will be (R + 4), (S + 4) and (T + 4).
Converting all ages in terms of S : (2S + 4), (S + 4), and (S + 7)

Now, let us check the options,
  • 1. (2S + 4) is not equal to 2(S + 4) ---> False
    2. Age difference will be same after 4 years ---> Always true
    3. (2S + 4) may or may not be greater than (S + 7) ---> Not always true
Hence, only 2 must be true.
hutch27 wrote:Would picking numbers be the fastest way to solve these types of word problems?
I would not suggest picking number for this problem.
Because the third option may or may not be true depending upon what numbers you pick.
If you pick R = 2, S = 1, and T = 4 --> Then 3 is not true
If you pick R = 8, S = 4, and T = 7 --> Then 3 is true
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by srcc25anu » Wed Apr 10, 2013 11:31 am
for St1: Rose is twice as old as Sam

2x + 4 = 2(x+4)
=> 2x + 4 = 2x + 8
NOT TRUE

St2: Sam is 3 years younger than Tina
True for any time

St3: Rose is OLDER than TINA

See Attached Table.
NOT TRUE

Only B is true.
Attachments
Sam Tina Rose.JPG
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by hutch27 » Wed Apr 10, 2013 12:06 pm
Anju@Gurome wrote:
hutch27 wrote:Today rose is twice as old as Sam and Sam is 3 years younger than Tina. If Rose, Same, and Tima are all alive 4 years from today, which of the following must be true on that day.

1- Rose is twice as old as sam
2- sam is 3 years younger than tina
3- rose is older than tina
Let us assume that today their ages are R, S, and T.
So, R = 2S and S = T - 3

After 4 years, their ages will be (R + 4), (S + 4) and (T + 4).
Converting all ages in terms of S : (2S + 4), (S + 4), and (S + 7)

Now, let us check the options,
  • 1. (2S + 4) is not equal to 2(S + 4) ---> False
    2. Age difference will be same after 4 years ---> Always true
    3. (2S + 4) may or may not be greater than (S + 7) ---> Not always true
Hence, only 2 must be true.
Ah, I see now where I went wrong. I actually applied the same method and let Rose's, sam's and Tina's age all be equal to R,S, and T, and then let R+4, S+4 and T+4 be equal to their ages in 4 years. The mistake I made was that I didn't put those respective ages in terms of S. Thanks a lot though, this really helped clarify things, especially since you were used the same method that I used.
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by Brent@GMATPrepNow » Wed Apr 10, 2013 1:22 pm
The technique that hutch27 refers to can be found in our free video here: https://www.gmatprepnow.com/module/gmat- ... ems?id=908

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by GMATGuruNY » Wed Apr 10, 2013 1:27 pm
hutch27 wrote:Today rose is twice as old as Sam and Sam is 3 years younger than Tina. If Rose, Same, and Tima are all alive 4 years from today, which of the following must be true on that day?

I - Rose is twice as old as sam
II - Sam is 3 years younger than tina
III - Rose is older than tina

A: I only
B: II only
C: III only
D: I and II
E: II and III

OA is B
Try to show that I, II and III DON'T have to be true.

Let S = 1.
Since Rose is twice as old, R = 2S = 2*1 = 2.
Since Sam is 3 years younger than Tina, T = S+3 = 1+3 = 4.
Ages in 4 years:
S = 1+4 = 5.
R = 2+4 = 6.
T = 4+4 = 8.

Since Rose is not twice as old as Sam, eliminate any answer choice that includes I (A and D).
Since Rose is not older than Tina, eliminate any remaining answer choice that includes III (C and E).

The correct answer is D.
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