Need help solving 3 quant DS questions Please :)

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rtaha2412: Senior | Next Rank: 100 Posts; Posts: 40; Joined: Fri Nov 27, 2009 7:48 pm; Thanked: 1 times

Need help solving 3 quant DS questions Please :)

by rtaha2412 » Tue Sep 28, 2010 5:54 pm

Hey everyone. If anyone could help show me the strategy to solve a few DS problems I would really appreciate it.

Question 1

By what percent has the price of an overcoat been reduced?
(1) The original price was $380.
(2) The original price was $50 more than the reduced price.

Question 2

Is x^2 equal to xy?
(1) x^2 - y^2 = (x + 5)(y - 5)
(2) x = y

Question 3
What was John's average driving speed in miles per hour during a 15-minute interval?
(1) He drove 10 miles during this interval.
(2) His maximum speed was 50 miles per hour and his minimum speed was 35 miles per hour during this interval.

Thanks so much!

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Source: Beat The GMAT — Data Sufficiency | Tue Sep 28, 2010 5:54 pm

GMAT/MBA Expert

Rahul@gurome: GMAT Instructor; Posts: 1179; Joined: Sun Apr 11, 2010 9:07 pm; Location: Milpitas, CA; Thanked: 447 times; Followed by:88 members

by Rahul@gurome » Tue Sep 28, 2010 6:37 pm

Solution to Q1:
The main question is asking that by what percent the price of an overcoat has reduced?
To solve this, we need the reduction in price and the original price because
(reduction in price)/(original price) * 100 will give us the required answer.

Let us first consider statement (1) alone.
It says original price was $380. But nothing is mentioned about reduction in price. So statement (1) alone is not sufficient to answer the question.

Next consider statement (2) alone.
It implies that reduction in price is $50. But we do not know the original price.
So (2) alone is not sufficient.

Next combine both he statements together and check. On combining we get that the percentage reduction in price is (50/380)*100.

Since both statements together are sufficient to answer the question, the correct answer is (C).

Rahul Lakhani
Quant Expert
Gurome, Inc.
https://www.GuroMe.com
On MBA sabbatical (at ISB) for 2011-12 - will stay active as time permits
1-800-566-4043 (USA)
+91-99201 32411 (India)

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GMAT/MBA Expert

Rahul@gurome: GMAT Instructor; Posts: 1179; Joined: Sun Apr 11, 2010 9:07 pm; Location: Milpitas, CA; Thanked: 447 times; Followed by:88 members

by Rahul@gurome » Tue Sep 28, 2010 6:52 pm

Solution to Q2:
The question is asking that Is x^2 = xy?
x^2 - xy = 0 implies x(x-y) = 0 or either x= 0 or x=y.
So the question can be reframed as Is x = 0 or x= y?

Let us first consider statement (1) alone.
It says x^2 - y^2 = (x+5)(y-5) = xy -5x+5y-25.
But this is not enough to tell us whether x= 0 or x = y or not.
So (1) alone is not sufficient to answer the question.

Next consider statement (2) alone.
It says x = y.
Then obviously x^2 = xy.
So (2) alone is sufficient to answer the question.

The correct answer is hence (B).

Rahul Lakhani
Quant Expert
Gurome, Inc.
https://www.GuroMe.com
On MBA sabbatical (at ISB) for 2011-12 - will stay active as time permits
1-800-566-4043 (USA)
+91-99201 32411 (India)

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monusangeeta: Senior | Next Rank: 100 Posts; Posts: 52; Joined: Mon Jun 07, 2010 8:36 pm; Location: India; Thanked: 3 times; Followed by:1 members; GMAT Score:720

by monusangeeta » Tue Sep 28, 2010 8:48 pm

For Question 3 answer should be A, please confirm.

Statement 1 => Total distance = 10 miles, Total time = 15 mins, avg speed = Distance/Time => Suff
Statement 2 => Max Speed, 50 m/hr and min Speed = 35 m/hr. but we dont know, whats the distance covered when speed was max and when speed was min. For avg speed = Total distance/Total time => INsuff.

Ans A.

Experts, please comment.

Thanks.