GMAT 2nd edition (little green book) Age question

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hutch27: Master | Next Rank: 500 Posts; Posts: 141; Joined: Fri Sep 07, 2012 10:25 pmFollowed by: 1 member; Location: NY; Thanked: 5 times

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

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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Source: Beat The GMAT — Problem Solving | Wed Apr 10, 2013 11:13 am

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Anju@Gurome: GMAT Instructor; Posts: 511; Joined: Wed Aug 11, 2010 9:47 amFollowed by: 86 members; Location: Delhi, India; Thanked: 344 times

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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srcc25anu: Master | Next Rank: 500 Posts; Posts: 423; Joined: Fri Jun 11, 2010 7:59 amFollowed by: 2 members; Location: Seattle, WA; Thanked: 86 times

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

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hutch27: Master | Next Rank: 500 Posts; Posts: 141; Joined: Fri Sep 07, 2012 10:25 pmFollowed by: 1 member; Location: NY; Thanked: 5 times

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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Brent@GMATPrepNow: GMAT Instructor; Posts: 16207; Joined: Mon Dec 08, 2008 6:26 pmFollowed by: 1268 members; Location: Vancouver, BC; Thanked: 5254 times; GMAT Score:770

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

Cheers,
Brent

Brent Hanneson - Creator of GMATPrepNow.com

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GMATGuruNY: GMAT Instructor; Posts: 15539; Joined: Tue May 25, 2010 12:04 pmFollowed by: 1906 members; Location: New York, NY; Thanked: 13060 times; GMAT Score:790

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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