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Register now and save up to $200 Available with Beat the GMAT members only code • 5 Day FREE Trial Study Smarter, Not Harder Available with Beat the GMAT members only code • 1 Hour Free BEAT THE GMAT EXCLUSIVE Available with Beat the GMAT members only code • Free Trial & Practice Exam BEAT THE GMAT EXCLUSIVE Available with Beat the GMAT members only code • Most awarded test prep in the world Now free for 30 days Available with Beat the GMAT members only code ## DS problems This topic has 6 member replies gabriel Legendary Member Joined 20 Dec 2006 Posted: 986 messages Followed by: 1 members Upvotes: 51 #### DS problems Wed Apr 18, 2007 11:05 am guys here are some good DS problems ... try and solve them .. q.) Train A leaves New York for Boston at 3 PM and travels at the constant speed of 100 mph. An hour later, it passes Train B, which is making the trip from Boston to New York at a constant speed. If Train B left Boston at 3:50 PM and if the combined travel time of the two trains is 2 hours, what time did Train B arrive in New York? (1) Train B arrived in New York before Train A arrived in Boston. (2) The distance between New York and Boston is greater than 140 miles. (A) Statement (1) alone is sufficient, but statement (2) alone is not sufficient. (B) Statement (2) alone is sufficient, but statement (1) alone is not sufficient. (C) BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient. (D) Each statement ALONE is sufficient. (E) Statements (1) and (2) TOGETHER are NOT sufficient. q.)Last Friday a certain shop sold 3/4 of the sweaters in its inventory. Each sweater sold or$20. What was the total revenue last Friday from the sale of these sweaters?

(1) When the shop opened last Friday, there were 160 sweaters in its inventory.
(2) All but 40 sweaters in the shop's inventory were sold last Friday.

A Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.
B Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.
C BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.
D EACH Statement ALONE is sufficient.
E Statements (1) and (2) TOGETHER are NOT sufficient.

q.) 8x(y^3) + 8 (x^3)y = [2(x^2)(y^2)] / [2^(-3)]

What is xy?

(1) y>x
(2) x<0

(A) Statement (1) alone is sufficient, but statement (2) alone is not sufficient.
(B) Statement (2) alone is sufficient, but statement (1) alone is not sufficient.
(C) BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.
(D) Each statement ALONE is sufficient.
(E) Statements (1) and (2) TOGETHER are NOT sufficient.

f2001290 Master | Next Rank: 500 Posts
Joined
10 Mar 2007
Posted:
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Sat Apr 21, 2007 2:48 am
1st and 3rd questions have broken my confidence.

Gabriel - what is the beat strategy to solve these sort of questions?

Prasanna Master | Next Rank: 500 Posts
Joined
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Posted:
418 messages
24
Sat Apr 21, 2007 4:19 pm
Thanks...How stupid I was

jayhawk2001 Community Manager
Joined
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Wed Apr 18, 2007 9:34 pm
Gabriel, I had a good mental workout . I seriously hope such
questions won't show up on GMAT or show up as experimental
questions.

gabriel wrote:
guys here are some good DS problems ... try and solve them ..

q.) Train A leaves New York for Boston at 3 PM and travels at the constant speed of 100 mph. An hour later, it passes Train B, which is making the trip from Boston to New York at a constant speed. If Train B left Boston at 3:50 PM and if the combined travel time of the two trains is 2 hours, what time did Train B arrive in New York?
(1) Train B arrived in New York before Train A arrived in Boston.

(2) The distance between New York and Boston is greater than 140 miles.

I think it should be D.

The question stem can be translated into equations of the form below --

x = distance between NY and BOS
B = speed of train B

We know x/100 + x/B = 2
and 100 + B/6 = x (for train B to reach NY, it has to travel x distance)

Using 2 in 1, we get

B^2 - 500B + 60000 = 0
B = 200 or 300
Correspondingly x = 150 or 800/6

1 tells us that B arrived before A. Only B=300 satisfies this.
If we choose B=200, A will arrive at 4:20 and B will arrive at 4:30
If we choose B=300, A will arrive at 4:30 and B will arrive at 4:20

2 tells us that x > 140 which implies it has to be 150 and hence
sufficient.

gabriel wrote:
q.)Last Friday a certain shop sold 3/4 of the sweaters in its inventory. Each sweater sold or $20. What was the total revenue last Friday from the sale of these sweaters? (1) When the shop opened last Friday, there were 160 sweaters in its inventory. (2) All but 40 sweaters in the shop's inventory were sold last Friday. 1 - sufficient. 3/4 * 160 * 20 is the revenue 2 - sufficient. 1/4 of inv = 40, so 3/4 = 120. So revenue = 120 * 20 Hence D gabriel wrote: q.) 8x(y^3) + 8 (x^3)y = [2(x^2)(y^2)] / [2^(-3)] What is xy? (1) y>x (2) x<0 We can translate the equation to 8xy (x^2 + y^2) = 8xy(2xy) 8xy*(x-y)^2 = 0 So, xy = 0 or (x-y)^2 = 0 1 - sufficient. x-y cannot be zero. So xy = 0 2 - insufficient. If x = y, then xy need not be zero. If x != y, then xy = 0 So, I think it should be A Prasanna Master | Next Rank: 500 Posts Joined 26 Feb 2007 Posted: 418 messages Upvotes: 24 Fri Apr 20, 2007 6:05 am Hi I am unable to understand the second equation you had derived in the first problem. "and 100 + B/6 = x (for train B to reach NY, it has to travel x distance)" Request you to help. Prasanna jayhawk2001 Community Manager Joined 28 Jan 2007 Posted: 789 messages Followed by: 1 members Upvotes: 30 Fri Apr 20, 2007 5:45 pm Prasanna wrote: Hi I am unable to understand the second equation you had derived in the first problem. "and 100 + B/6 = x (for train B to reach NY, it has to travel x distance)" Request you to help. Prasanna x is the total distance between NY and BOS. We know the 2 trains meet at a point which is 100 miles from NY. We also know that B * 10min/60min is the total distance that B would have traveled from BOS to the point in between. So, 100 + B/6 = x gabriel Legendary Member Joined 20 Dec 2006 Posted: 986 messages Followed by: 1 members Upvotes: 51 Sat Apr 21, 2007 1:14 am jayhawk2001 wrote: Gabriel, I had a good mental workout . I seriously hope such questions won't show up on GMAT or show up as experimental questions. gabriel wrote: guys here are some good DS problems ... try and solve them .. q.) Train A leaves New York for Boston at 3 PM and travels at the constant speed of 100 mph. An hour later, it passes Train B, which is making the trip from Boston to New York at a constant speed. If Train B left Boston at 3:50 PM and if the combined travel time of the two trains is 2 hours, what time did Train B arrive in New York? (1) Train B arrived in New York before Train A arrived in Boston. (2) The distance between New York and Boston is greater than 140 miles. I think it should be D. The question stem can be translated into equations of the form below -- x = distance between NY and BOS B = speed of train B We know x/100 + x/B = 2 and 100 + B/6 = x (for train B to reach NY, it has to travel x distance) Using 2 in 1, we get B^2 - 500B + 60000 = 0 B = 200 or 300 Correspondingly x = 150 or 800/6 1 tells us that B arrived before A. Only B=300 satisfies this. If we choose B=200, A will arrive at 4:20 and B will arrive at 4:30 If we choose B=300, A will arrive at 4:30 and B will arrive at 4:20 2 tells us that x > 140 which implies it has to be 150 and hence sufficient. gabriel wrote: q.)Last Friday a certain shop sold 3/4 of the sweaters in its inventory. Each sweater sold or$20. What was the total revenue last Friday from the sale of these sweaters?

(1) When the shop opened last Friday, there were 160 sweaters in its inventory.
(2) All but 40 sweaters in the shop's inventory were sold last Friday.
1 - sufficient. 3/4 * 160 * 20 is the revenue
2 - sufficient. 1/4 of inv = 40, so 3/4 = 120. So revenue = 120 * 20

Hence D

gabriel wrote:
q.) 8x(y^3) + 8 (x^3)y = [2(x^2)(y^2)] / [2^(-3)]

What is xy?

(1) y>x
(2) x<0

We can translate the equation to

8xy (x^2 + y^2) = 8xy(2xy)
8xy*(x-y)^2 = 0

So, xy = 0 or (x-y)^2 = 0

1 - sufficient. x-y cannot be zero. So xy = 0

2 - insufficient. If x = y, then xy need not be zero. If x != y, then xy = 0

So, I think it should be A
excellent dood .... u got all of them right ... seems like u ready to take the gmat on (head on) ... these were q's that i got form some other forums ( no copyright issues ) ... and they are defnitely in the range of 730 -760 ( i just loved the first q) .. so i dont think u shuld be really worried abt the quant part anymore ..

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