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The average score of x number of exams is y. When an additional exam

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The average score of x number of exams is y. When an additional exam [#permalink]

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New post 08 Oct 2014, 13:23
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Tough and Tricky questions: Statistics



The average score of x number of exams is y. When an additional exam of score z is added in, does the average score of the exams increase by 50%?

(1) 3x = y
(2) 2z - 3y = xy
[Reveal] Spoiler: OA

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Re: The average score of x number of exams is y. When an additional exam [#permalink]

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New post 08 Oct 2014, 22:00
Bunuel wrote:

Tough and Tricky questions: Statistics



The average score of x number of exams is y. When an additional exam of score z is added in, does the average score of the exams increase by 50%?

(1) 3x = y
(2) 2z - 3y = xy


B.

The questions can be mathematically represented as:

(xy+z)/(x+1) = 1.5y --- (A)

1) 3x=y
clearly insufficient as we have no info about z.

2) 2z-3y=xy
this is nothing but the simplified form of equation (A)
sufficient.
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The average of a set of x exam scores is y. When an additional exam of [#permalink]

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New post 23 Mar 2017, 22:55
The average of a set of x exam scores is y. When an additional exam of score z is added to the set, does the average score of the exams increase by 50%?

(1) \(3 x = y\)
(2) \(2 z – 3 y = xy\)
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Re: The average of a set of x exam scores is y. When an additional exam of [#permalink]

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New post 23 Mar 2017, 23:16
Sum of the exam scores = xy
When new score z is introduced, sum is xy+z
Avg =( xy+z)/x+1
Question is asking if (xy+z)/x+1 = 150% of y
On solving, we get xy = 2z-3y, which is given in statement b
Hence B.

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Re: The average score of x number of exams is y. When an additional exam [#permalink]

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New post 24 Mar 2017, 00:06
ziyuen wrote:
The average of a set of x exam scores is y. When an additional exam of score z is added to the set, does the average score of the exams increase by 50%?

(1) \(3 x = y\)
(2) \(2 z – 3 y = xy\)


Merging topics. Please refer to the discussion above.
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Collection of Questions:
PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat

DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.


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Re: The average score of x number of exams is y. When an additional exam [#permalink]

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New post 24 Mar 2017, 01:01
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Alternate method:

Let number of exams = x = 10
average = y = 50

Question: Is (500 + z)/11 = 75?

St1: x = 3y --> Clearly insufficient as we do not know anything about z.

St2: z = (xy + 3y)/2 = (500 + 150)/2
We know the value of z.
Sufficient.

Answer: B

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Re: The average score of x number of exams is y. When an additional exam [#permalink]

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New post 11 Sep 2017, 04:31
Bunuel wrote:

Tough and Tricky questions: Statistics



The average score of x number of exams is y. When an additional exam of score z is added in, does the average score of the exams increase by 50%?

(1) 3x = y
(2) 2z - 3y = xy


St 1

We know nothing about Z

St 2

Holds true for all scenarios for example

x=3 ,y=4

x=5, y=6

B

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Re: The average score of x number of exams is y. When an additional exam   [#permalink] 11 Sep 2017, 04:31
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