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D01-19

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D01-19  [#permalink]

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New post 16 Sep 2014, 00:12
00:00
A
B
C
D
E

Difficulty:

  45% (medium)

Question Stats:

67% (00:41) correct 33% (00:57) wrong based on 156 sessions

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Re D01-19  [#permalink]

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New post 16 Sep 2014, 00:12
Official Solution:


First of all:

The median of a set with odd # of terms is just a middle term (when ordered in ascending/descending order).

The median of a set with even # of terms is the average of two middle terms (when ordered in ascending/descending order).

Next, one of the most important properties of evenly spaced set (aka arithmetic progression):

In any evenly spaced set the arithmetic mean (average) is equal to the median and can be calculated by the formula \(mean=median=\frac{a_1+a_n}{2}\), where \(a_1\) is the first term and \(a_n\) is the last term. Given the set \(\{7,11,15,19\}\), \(mean=median=\frac{7+19}{2}=13\).

(1) All members of \(S\) are consecutive multiples of 3. This statement says that \(S\) is an evenly spaced set, thus its mean equals to its median. Sufficient.

(2) The sum of all members of \(S\) equals 75. Clearly insufficient, consider two sets \(\{25, 25, 25\}\) and \(\{0, 0, 75\}\).


Answer: A
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Re: D01-19  [#permalink]

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New post 09 Oct 2015, 06:47
Bunuel wrote:
Official Solution:


First of all:

The median of a set with odd # of terms is just a middle term (when ordered in ascending/descending order).

The median of a set with even # of terms is the average of two middle terms (when ordered in ascending/descending order).

Next, one of the most important properties of evenly spaced set (aka arithmetic progression):

In any evenly spaced set the arithmetic mean (average) is equal to the median and can be calculated by the formula \(mean=median=\frac{a_1+a_n}{2}\), where \(a_1\) is the first term and \(a_n\) is the last term. Given the set \(\{7,11,15,19\}\), \(mean=median=\frac{7+19}{2}=13\).

(1) All members of \(S\) are consecutive multiples of 3. This statement says that \(S\) is an evenly spaced set, thus its mean equals to its median. Sufficient.

(2) The sum of all members of \(S\) equals 75. Clearly insufficient, consider two sets \(\{25, 25, 25\}\) and \(\{0, 0, 75\}\).


Answer: A



Don't mean to sound picky but is this sentence correct? "evenly spaced set (aka arithmetic progression)" don't evenly spaced sets include geometric progressions and arithmetic progressions?
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Re: D01-19  [#permalink]

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New post 09 Oct 2015, 08:09
Jonas84 wrote:
Bunuel wrote:
Official Solution:


First of all:

The median of a set with odd # of terms is just a middle term (when ordered in ascending/descending order).

The median of a set with even # of terms is the average of two middle terms (when ordered in ascending/descending order).

Next, one of the most important properties of evenly spaced set (aka arithmetic progression):

In any evenly spaced set the arithmetic mean (average) is equal to the median and can be calculated by the formula \(mean=median=\frac{a_1+a_n}{2}\), where \(a_1\) is the first term and \(a_n\) is the last term. Given the set \(\{7,11,15,19\}\), \(mean=median=\frac{7+19}{2}=13\).

(1) All members of \(S\) are consecutive multiples of 3. This statement says that \(S\) is an evenly spaced set, thus its mean equals to its median. Sufficient.

(2) The sum of all members of \(S\) equals 75. Clearly insufficient, consider two sets \(\{25, 25, 25\}\) and \(\{0, 0, 75\}\).


Answer: A



Don't mean to sound picky but is this sentence correct? "evenly spaced set (aka arithmetic progression)" don't evenly spaced sets include geometric progressions and arithmetic progressions?


An evenly spaced set is one in which the gap between each successive element in the set is equal.

A geometric progression is NOT an evenly spaced set. For example, 2, 4, 8, 16, 32, ... is NOT evenly spaced because the gap between each successive element in the set is NOT equal.

Hope it's clear.
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Re: D01-19  [#permalink]

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New post 10 Oct 2016, 12:27
1
Bunuel
what about negative multiples??
what if the set is {-6,-3,0,3} is this not consecutive multiples?? in this case mean=-2 and median is -1.5
I think Statement 1 should say positive consecutive multiples? OR is that in GMAT multiples of any no. are always taken as positive multiples??
thanks
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Re: D01-19  [#permalink]

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New post 11 Oct 2016, 06:25
deepak268 wrote:
Bunuel
what about negative multiples??
what if the set is {-6,-3,0,3} is this not consecutive multiples?? in this case mean=-2 and median is -1.5
I think Statement 1 should say positive consecutive multiples? OR is that in GMAT multiples of any no. are always taken as positive multiples??
thanks


We can consider negative integers as multiples too. For example, -4 is a multiple of 2.

The problem is that the mean of {-6,-3,0,3} is -1.5, not -2.
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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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D01-19  [#permalink]

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New post 10 Jun 2018, 07:11
Statement 1.. All the numbers could also be 0 right? Therefore, I'd go with C
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Re: D01-19  [#permalink]

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New post 10 Jun 2018, 08:08
drithisunil wrote:
Statement 1.. All the numbers could also be 0 right? Therefore, I'd go with C


It's given in statement 1 that
All members of S are consecutive multiples of 3
And this doesn't seem to be S = {0,0,0,0,0,0....}
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Re: D01-19 &nbs [#permalink] 10 Jun 2018, 08:08
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