OG Green Q76

Expert replies

umaa: Legendary Member; Posts: 727; Joined: Sun Jun 08, 2008 9:32 pmFollowed by: 1 member; Thanked: 8 times

by umaa » Wed Jan 14, 2009 12:29 pm

Today Rose is twice as old as Sam and Sam is 3 years younger than Tina. If Rose, Sam, and Tina 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 only
E. II and III only

I chose E.

My explanation:

Assume, R 50.

R=2S
So, S = 25

S = T-3
So, T = 28

After 4 years,

R = 54

S = 29

T = 32

They satisfy both II and III conditions. Let me know if I'm wrong.

Source: Beat The GMAT — Problem Solving | Wed Jan 14, 2009 12:29 pm

Stuart@KaplanGMAT: GMAT Instructor; Posts: 3224; Joined: Tue Jan 08, 2008 2:40 pmFollowed by: 614 members; Location: Toronto; Thanked: 1710 times; GMAT Score:800

Re: OG Green Q76

by Stuart@KaplanGMAT » Wed Jan 14, 2009 12:59 pm

umaa wrote:Today Rose is twice as old as Sam and Sam is 3 years younger than Tina. If Rose, Sam, and Tina 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 only
E. II and III only

I chose E.

My explanation:

Assume, R 50.

R=2S
So, S = 25

S = T-3
So, T = 28

After 4 years,

R = 54

S = 29

T = 32

They satisfy both II and III conditions. Let me know if I'm wrong.

You answered the question "which of the following COULD be true on that day". However, the question is asking about what "MUST" be true.

If you pick different numbers, you'll see that III is not a MUST be true.

For example, if we let:

R = 2
S = 1
T = 4

we still follow the original rules, but we see that Rose is NOT older than Tina.

Accordingly, only statement II is a "MUST" be true: choose (B).

Stuart Kovinsky | Kaplan GMAT Faculty | Toronto

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umaa: Legendary Member; Posts: 727; Joined: Sun Jun 08, 2008 9:32 pmFollowed by: 1 member; Thanked: 8 times

by umaa » Wed Jan 14, 2009 1:01 pm

Got it. Thx..

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