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PS Expert - Math Revolution: Ask Me Anything about GMAT PS
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MathRevolution
Math Revolution GMAT Instructor
Joined: 16 Aug 2015
Posts: 11549
GMAT 1: 760 Q51 V42
GPA: 3.82
Re: PS Expert - Math Revolution: Ask Me Anything about GMAT PS [#permalink] New post  16 Jul 2021, 08:59
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Que: The trader first decreased the selling price of a car by 30 percent and then increased by 30 percent. Which of the following represents the final percent change in the selling price of the bicycle?

(A) 9% less
(B) 0%
(C) 9% more
(D) 91% less
(E) 91% more
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MathRevolution
Math Revolution GMAT Instructor
Joined: 16 Aug 2015
Posts: 11549
GMAT 1: 760 Q51 V42
GPA: 3.82
Re: PS Expert - Math Revolution: Ask Me Anything about GMAT PS [#permalink] New post  17 Jul 2021, 21:15
Expert Reply
MathRevolution wrote:
Que: The trader first decreased the selling price of a car by 30 percent and then increased by 30 percent. Which of the following represents the final percent change in the selling price of the bicycle?

(A) 9% less
(B) 0%
(C) 9% more
(D) 91% less
(E) 91% more



Solution: Let us apply the IVY approach to solve the question. As we are dealing with percentage, then let the original price of a car be $100.

Price after price reduced by 30%: (100 - 30)% of $100

=> \((\frac{70}{100})*$100 = $70\)

Price after the new price increased by 30%: (100 + 30)% of $70

=> \((\frac{130}{100})$70 = $91\)

As the base price is $100, the final price would be 91% of the base price.

Since Percent change = \(\frac{(After - Before)}{Before} * 100\)(%) and $100 (Before) and $91 (After),

We get Percent change = \(\frac{($91 - $100)}{$100} * 100\)(%) =\( \frac{(-9)}{100} * 100\)(%) = -9%

Therefore, A is the correct answer.

Answer A
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MathRevolution: The World's Most "Complete" GMAT Math Course!
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MathRevolution
Math Revolution GMAT Instructor
Joined: 16 Aug 2015
Posts: 11549
GMAT 1: 760 Q51 V42
GPA: 3.82
Re: PS Expert - Math Revolution: Ask Me Anything about GMAT PS [#permalink] New post  17 Jul 2021, 21:24
Expert Reply
Que: An instructor gave the same test to three groups: A, B, and C. The average (arithmetic mean) scores for the three groups were 40, 50, and 60, respectively. The ratio of the numbers of candidates in the A, B, and C groups were 1 : 3: 5, respectively. What was the average score for the three groups combined?

(A) 21.11
(B) 36.66
(C) 50
(D) 54.44
(E) 80
_________________
MathRevolution: The World's Most "Complete" GMAT Math Course!
Score an excellent Q49-51 just like 70% of our students.
[Free] Full on-demand course (7 days) - 100 hours of video lessons, 490 lesson topics, and 2,000 questions.
[Course] Starting at $79 for on-demand and $60 for tutoring per hour and $390 only for Live Online
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MathRevolution
Math Revolution GMAT Instructor
Joined: 16 Aug 2015
Posts: 11549
GMAT 1: 760 Q51 V42
GPA: 3.82
Re: PS Expert - Math Revolution: Ask Me Anything about GMAT PS [#permalink] New post  19 Jul 2021, 01:16
Expert Reply
MathRevolution wrote:
Que: An instructor gave the same test to three groups: A, B, and C. The average (arithmetic mean) scores for the three groups were 40, 50, and 60, respectively. The ratio of the numbers of candidates in the A, B, and C groups were 1 : 3: 5, respectively. What was the average score for the three groups combined?

(A) 21.11
(B) 36.66
(C) 50
(D) 54.44
(E) 80



Solution: Let the number of candidates in groups A, B, and C be 1k, 3k, and 5k, respectively, where ‘k's is a constant of proportionality.

The average (arithmetic mean) scores for the three groups were 40, 50, and 60, respectively. The combined average for the three groups is

=> \(\frac{[ (40 * k) + (50 * 3k) + (60 * 5k)] }{ (k + 3k + 5k)}\)

=> \(\frac{[(40k + 150k + 300k)]}{ (9k)}\)

=> \(\frac{490k }{ 9k} = 54.44\)

Therefore, D is the correct answer.

Answer D
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MathRevolution
Math Revolution GMAT Instructor
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Posts: 11549
GMAT 1: 760 Q51 V42
GPA: 3.82
Re: PS Expert - Math Revolution: Ask Me Anything about GMAT PS [#permalink] New post  19 Jul 2021, 01:22
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Que: A color “code” is defined as a sequence of four dots arranged in a row. Each dot is colored either “blue” or “green.” How many distinct codes can be formed?

(A) 2
(B) 4
(C) 8
(D) 16
(E) 32
_________________
MathRevolution: The World's Most "Complete" GMAT Math Course!
Score an excellent Q49-51 just like 70% of our students.
[Free] Full on-demand course (7 days) - 100 hours of video lessons, 490 lesson topics, and 2,000 questions.
[Course] Starting at $79 for on-demand and $60 for tutoring per hour and $390 only for Live Online
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User avatar
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MathRevolution
Math Revolution GMAT Instructor
Joined: 16 Aug 2015
Posts: 11549
GMAT 1: 760 Q51 V42
GPA: 3.82
Re: PS Expert - Math Revolution: Ask Me Anything about GMAT PS [#permalink] New post  19 Jul 2021, 23:28
Expert Reply
MathRevolution wrote:
Que: A color “code” is defined as a sequence of four dots arranged in a row. Each dot is colored either “blue” or “green.” How many distinct codes can be formed?

(A) 2
(B) 4
(C) 8
(D) 16
(E) 32



Solution: The first dot can use Blue or Green, the second dot also can use Blue or Green, the third dot also can use Blue or Green and the Fourth dot also can use Blue or Green, so 2 * 2 * 2 * 2 = 16

Therefore, D is the correct answer.

Answer D
_________________
MathRevolution: The World's Most "Complete" GMAT Math Course!
Score an excellent Q49-51 just like 70% of our students.
[Free] Full on-demand course (7 days) - 100 hours of video lessons, 490 lesson topics, and 2,000 questions.
[Course] Starting at $79 for on-demand and $60 for tutoring per hour and $390 only for Live Online
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User avatar
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MathRevolution
Math Revolution GMAT Instructor
Joined: 16 Aug 2015
Posts: 11549
GMAT 1: 760 Q51 V42
GPA: 3.82
Re: PS Expert - Math Revolution: Ask Me Anything about GMAT PS [#permalink] New post  19 Jul 2021, 23:33
Expert Reply
Que: Find the number of keystrokes required to type numbers from 1 to 900?

(A) 2,583
(B) 2,589
(C) 2,590
(D) 2,592
(E) 2,593
_________________
MathRevolution: The World's Most "Complete" GMAT Math Course!
Score an excellent Q49-51 just like 70% of our students.
[Free] Full on-demand course (7 days) - 100 hours of video lessons, 490 lesson topics, and 2,000 questions.
[Course] Starting at $79 for on-demand and $60 for tutoring per hour and $390 only for Live Online
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Re: PS Expert - Math Revolution: Ask Me Anything about GMAT PS [#permalink]
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