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Tough DS problems- help needed

by intenseCK » Wed Apr 11, 2012 2:48 am
Q1- Lines n and p lie in xy plane. is slope of line n less then slope of line p?
a. lines n and p intersect at (5,1)
b. Y-intercept of line n is greater then y-intercept of line p

Q2-if the average of 5 numbers, X,7,2,16, 11= median, what is X?
a. 7<x>11
b. X is median of 5 numbers.

Q3- If everyone was charged the same fee, how many people came?
a. if the fee had been %.75 less and 100 more ppl came the club wud hv received the same amount.
b. if fee had been 1.50$ more and 100 fewer ppl came, club wud hv got the same amount?

Q4- Some water was removed from each of 6 tanks. if standard deviation of the volumes of water at the beginning was 10 gallons, what was the standard deviation of the vloumes at the end?
a. for each tank, 30% of the water at the beginning was removed
b. the avg volume of water in the taks at the end was 63 gallons.

Q5.
Image
in this figure, what is the ratio of KN/MN?
a. perimeter of KLMN is 30
b. All three rectangular sections have the same dimensions.
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by GMATGuruNY » Wed Apr 11, 2012 7:04 am
intenseCK wrote: Q3- If everyone was charged the same fee, how many people came?
a. if the fee had been %.75 less and 100 more ppl came the club wud hv received the same amount.
b. if fee had been 1.50$ more and 100 fewer ppl came, club wud hv got the same amount?
I posted a solution here:

https://www.beatthegmat.com/how-many-peo ... 90830.html
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by GMATGuruNY » Wed Apr 11, 2012 7:06 am
During an experiment, some water was removed from each of 6 water tanks. If the standard deviation of the volumes of water in the tanks at the beginning of the experiment was 10 gallons, what was the standard deviation of the volumes of water in the tanks at the end of the experiment?
(1) For each tank, 30 percent of the volume of water that was in the tank at the beginning of the experiment was removed during the experiment.
(2) The average (arithmetic mean) volume of water in the tanks at the end of the experiment was 63 gallons.
If every element in a set is increased or decreased by the same CONSTANT, then the standard deviation DOES NOT CHANGE.

If every element in a set is increased or decreased by the SAME PERCENTAGE, then the standard deviation WILL CHANGE BY THE SAME PERCENTAGE.

Statement 1: For each tank, 30 percent of the volume of water that was in the tank at the beginning of the experiment was removed during the experiment.
Since every value was decreased by 30%, the SD at the end of the experiment was 70% of the old SD:
.7(10) = 7.
SUFFICIENT.

Statement 2: The average (arithmetic mean) volume of water in the tanks at the end of the experiment was 63 gallons.
No way to determine the SD.
INSUFFICIENT.

The correct answer is A.
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by GmatKiss » Wed Apr 11, 2012 11:07 am
Q2-if the average of 5 numbers, X,7,2,16, 11= median, what is X?
a. 7<x>11
b. X is median of 5 numbers.

IMO : B
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by intenseCK » Thu Apr 12, 2012 5:13 am
GmatKiss wrote:Q2-if the average of 5 numbers, X,7,2,16, 11= median, what is X?
a. 7<x>11
b. X is median of 5 numbers.

IMO : B
please can u explain?
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by intenseCK » Thu Apr 12, 2012 5:18 am
can someone post explainations to the remaining questions as well..TIA
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by intenseCK » Thu Apr 12, 2012 5:20 am
can someone post explainations to the remaining questions as well..TIA
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by intenseCK » Thu Apr 12, 2012 5:24 am
can someone post explainations to the remaining questions as well..TIA
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by Shalabh's Quants » Thu Apr 12, 2012 7:45 am
intenseCK wrote:
GmatKiss wrote:Q2-if the average of 5 numbers, X,7,2,16, 11= median, what is X?
a. 7<x>11
b. X is median of 5 numbers.

IMO : B
please can u explain?
Since From Stat.1, we cannot conclude about the position of X.

Given is 7<X>11. It means X is greater than 7 & 11 both. There seem to be some mistake in the problem as stating X>7 will imply that X has an open interval, stating X may be greater than X>11 too.

However if we insist on 7<X>11 than Stat. 1 is insufficient to conclude as we are not sure if X will lie between 7 & 11, 11 & 16, or beyond.

Stat. 2..

=> 'X is median of 5 numbers' clearly suggests that X is the 3rd element if we arrange 5 nos.in a ascending order i.e. 16, 11, X, 7 & 2.

=> Given is X = Median = average, so X = (16+11+X+7+2)/5; X = 9.

Ans B.

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by Shalabh's Quants » Thu Apr 12, 2012 8:27 am
Q1- Lines n and p lie in xy plane. is slope of line n less then slope of line p?
a. lines n and p intersect at (5,1)
b. Y-intercept of line n is greater then y-intercept of line p
say Eqn. of line n is y=m'x+c' & for line p is y=m''x+c''.

Stat. 1...

As both pass through point (5,1), hence we can write...

=> 1=5m'+c'------(1) &
1=5m''+c''------(2)

We cannot conclude as no information abt intercepts given.

Stat. 2...

=> Given is |c'|>|c''|; taking absolute value so that we can ignore sign of intercepts.

can't conclude as there may be infinite no. of lines having slope greater/lesser than each other.

Stat. 1 & 2...

=> By equating eqn. 1 & 2, we get,

=> 5(m'-m'')=|c''|-|c'| => (m'-m'')= (|c''|-|c'|)/5

as |c'|>|c''|, hence (m'-m'')< 0. So m' < m''.

Ans. C.

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by Shalabh's Quants » Thu Apr 12, 2012 8:32 am
Q5.
Image
in this figure, what is the ratio of KN/MN?
a. perimeter of KLMN is 30
b. All three rectangular sections have the same dimensions.[/quote]

What is K, M & N?
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