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prep questions

by bww » Sun May 06, 2007 4:58 pm
Can someone please give a quick explanation? Thanks.

1)
Month Average Price/Dozen
April $1.26
May $1.20
June $1.08

The table above shows the average (arithm mean) price per dozen of the large grade A eggs sold in a store during three successive months. If 2/3 as many dozen were sold in April as in May, and twice as many were sold in June, what was the average price per dozen of the eggs sold over the three-month period?

(A) $1.08
(B) $1.10
(C) $1.14
(D) $1.16
(E) $1.18

2)
If y does not equal 3 and (3x)/y is a prime integer greater than 2, which of the following must be true?

I. x = y
II. y = 1
III. x and y are prime integers

(A) None
(B) I only
(C) II only
(D) III only
(E) I and III

Official answers are D and A, respectively.
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Re: prep questions

by jayhawk2001 » Sun May 06, 2007 5:27 pm
bww wrote:Can someone please give a quick explanation? Thanks.

1)
Month Average Price/Dozen
April $1.26
May $1.20
June $1.08

The table above shows the average (arithm mean) price per dozen of the large grade A eggs sold in a store during three successive months. If 2/3 as many dozen were sold in April as in May, and twice as many were sold in June, what was the average price per dozen of the eggs sold over the three-month period?
Let x be the number of dozen eggs sold in may

Avg price = total sale price / total eggs sold
= (2/3*x*1.26 + x*1.2 + 2*x*1.08 ) / (2/3x + x + 2x)
= 4.2*x / (11/3*x)
= 1.145

I'm not getting D
bww wrote: 2)
If y does not equal 3 and (3x)/y is a prime integer greater than 2, which of the following must be true?

I. x = y
II. y = 1
III. x and y are prime integers

(A) None
(B) I only
(C) II only
(D) III only
(E) I and III

Official answers are D and A, respectively.
3x/y is prime.

Take x = 1 and y = 3/7.

I, II and III don't hold true for the above but 3x/y = 7 > 2 and is prime

Hence A
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by Cybermusings » Tue May 08, 2007 2:49 am
Let 6 dozens be sold in May...So 2/3*6 = 4 will be sold in April and 12 will be sold in June
So average = (1.26*4)+(1.20*6)+(12*1.08 ) / 22
= 25.20/22 = 1.14 (Approx)
Last edited by Cybermusings on Tue May 08, 2007 2:56 am, edited 1 time in total.
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by Cybermusings » Tue May 08, 2007 2:56 am
Statement II : Can't be true...If y = 1 and x = 1 then 3x/y becomes a prime integer greater than 2. However, if y = 1 and x = 4, then 3x/y = 3*4 = 12/1 which is not prime
Statement I : Has to be always true ; otherwise 3x/y will not be a prime integer. try substituting any value where x is not equal to y. Hence x = y
Statement III : If x = y then x = y = 1,2,4,5,6 anything; and still 3x/y will be a prime integer greater than 2. Hence III is not true always

So answer is I only
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by jayhawk2001 » Tue May 08, 2007 9:04 pm
Cybermusings wrote:Statement II : Can't be true...If y = 1 and x = 1 then 3x/y becomes a prime integer greater than 2. However, if y = 1 and x = 4, then 3x/y = 3*4 = 12/1 which is not prime
Statement I : Has to be always true ; otherwise 3x/y will not be a prime integer. try substituting any value where x is not equal to y. Hence x = y
Statement III : If x = y then x = y = 1,2,4,5,6 anything; and still 3x/y will be a prime integer greater than 2. Hence III is not true always

So answer is I only
For I, how about x = 1 and y = 3/7. Since we aren't given that x and y are
integers, I'm not sure if we can make the assumption (i.e. x=y)

Please correct if I have it interpreted it wrongly.
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by crackitpal » Mon Aug 20, 2007 5:01 pm
so what is the correct answer for Eggs problem ? is it (C) or (D) ?
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by dabulaila » Tue Aug 21, 2007 7:38 am
I have posted the same question and someone answered it, here is the solution


Given:
Aa,Am,Aj=(1.26,1.20,1.080 )
Sa=Sm
Sj=2Sa

Total Sales=Sa+Sm+Sj
=Sa+Sa+2Sa
=4Sa

3-Month Avg=Sales Price*Sale/Total Sales
=(Sa*Aa + Sm * Am + Sj * Aj) / ( Sa + Sm + Sj)
= (Sa * Aa + Sa * Am + 2Sa * Aj ) / 4Sa
=Sa (Aa+Am+2Aj)/4 (Sa)
= (Aa+Am+2Aj)/4
=(1.26+1.20+2*1.080)/4
=1.155
~=1.16 = D
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by arora007 » Wed Dec 15, 2010 9:55 am
Good questions...
I believe they are from
https://gmat1000ps.blocked
SECTION 1
Question number 19 and 20
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by gupta.ansh13 » Thu Dec 16, 2010 1:09 am
Let us consider

April $1.26 No of Eggs = 4
May $1.20 6
June $1.08 2

Therefore total no of eggs = 4+6+2=12
Total Price 1.26*4+1.20*6+1.08*2=5.04+7.2+2.16=14.4

Average = 14.4/12=1.2
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by arora007 » Thu Dec 16, 2010 9:48 pm
gupta.ansh13 wrote:Let us consider

April $1.26 No of Eggs = 4
May $1.20 6
June $1.08 2

Therefore total no of eggs = 4+6+2=12
Total Price 1.26*4+1.20*6+1.08*2=5.04+7.2+2.16=14.4

Average = 14.4/12=1.2
The number of eggs in June is incorrect. try solving again...
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