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Please explain on some GMAT prep1 quant questions

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Please explain on some GMAT prep1 quant questions

by nothinglessthan780 » Mon Nov 24, 2008 12:38 am
Hi folks...I am not able to get the correct answer for the following questions on Gmatprep1..somebody please explain.

1.For all positive integers m,[m] = 3m when m is odd and [m]=1/2m when m is even.Which of the following is equivalent to [9]*[6]
A)81
B)54
C)36
D)27
E)18

Following the given info..i substituted m for 9 and since9 is odd [m] became 3*9 = 27 and m for 6 and since 6 is even it became (1/2)*6=3
therefore [9]*[6]=27*3=81 which is incorrect...
Anyone with an idea why D)27 is the correct answer?

2.Circular gears P and Q start rotating at the same time at constant speeds.Gear P makes 10 revolutions per minute and gear Q makes 40 revolutions per minute.How many seconds after the gears rotating will gear Q have made exactly 6 more revolutions than gear P?
No idea on how to solve this question.The correct given answer is 12.


Do explanations for GMATPrep Tests exist?
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by orel » Mon Nov 24, 2008 1:15 am
HI!

i got 81 for the 1st problem. have no idea why it is incorrect.


the second question:

imagine that the number of rotations is distance.

Velocity of the Gear P is 10rotations/min
Velocity of Gear Q is 40roations/min

How many seconds after the gears rotating will gear Q have made exactly 6 more revolutions than gear P means:

rotations of Gear P + 6 = rotations of Gear Q

Using the Formula: S=VT (S-distance, V-velocity, T-time)
we can find that:

10T+6=40T
30T=6
T=1/5 min

as the question asks the time in seconds:

T=1/5*60=12sec.

am i right? :)
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GMAT Prep Questions Explanations

by nothinglessthan780 » Mon Nov 24, 2008 2:40 am
Hi Feruza,

Thanks for the explanation on the questions on gear P and Q...I have understood the method you have used...I think the answer is right.

One more question..

Q.In a certain deck of cards each card has a positive integer written on it.In a multiplication game,a child draws a card and multiplies the integer on the card by the next larger integer.If each possible product is between 15 and 200, then the least and greatest integers on the cards could be?
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by orel » Mon Nov 24, 2008 3:03 am
my approach to the last question:

the smallest integer on the cards can be determined in following way:

a(a+1)>=15

a^2+a-15>=0
the smallest positive integer satisfying the inequality is 4

the largest integer on the cards can be determined in following way:

b(b+1)<=200

b^2+b-200<=0
the largest positive integer satisfying the inequality is 13

So, 4 and 13
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by jimmiejaz » Mon Nov 24, 2008 6:07 am
For the 1st question D is the correct answer.
The question asks which of the following is equivalent to .....
yes, indeed you will get 81 by solving wats given in the question. But, this is a classic trap.

How will you get 81 from the list of choices.
You will get by 27 since 27 is odd and when odd we use 3m.
So, by using 27, we get 3*27=81 which we got initially.
So, the correct ans is D and not A.

Hope it helps.
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by nothinglessthan780 » Mon Nov 24, 2008 12:15 pm
Feruza Matyakubova wrote:my approach to the last question:

the smallest integer on the cards can be determined in following way:

a(a+1)>=15

a^2+a-15>=0
the smallest positive integer satisfying the inequality is 4

the largest integer on the cards can be determined in following way:

b(b+1)<=200

b^2+b-200<=0
the largest positive integer satisfying the inequality is 13

So, 4 and 13
Thanks for the explanation......the equation is clearer now...how do you solve for an inequality a^2+a-15>=0 to get 4...Tried factorizing, got stuck?
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by nothinglessthan780 » Mon Nov 24, 2008 12:25 pm
jimmiejaz wrote:For the 1st question D is the correct answer.
The question asks which of the following is equivalent to .....
yes, indeed you will get 81 by solving wats given in the question. But, this is a classic trap.

How will you get 81 from the list of choices.
You will get by 27 since 27 is odd and when odd we use 3m.
So, by using 27, we get 3*27=81 which we got initially.
So, the correct ans is D and not A.

Hope it helps.
Thanks for your response
I still cant get what the trap is...i thought equivalent to [9]*[6] means substitution,and getting 81......does it mean you just consider the first part of the question i.e [m]=3m and ignore the [m]=1/2 m despite having [9]* [6]?
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by nothinglessthan780 » Mon Nov 24, 2008 12:32 pm
Hi folks...yet another question i cant figure out how to resolve..please help..

Q)2^x-2^x-2=3(2^13).What is the value of x?
A)9
B)11
C)13
D)15
E)17
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by nothinglessthan780 » Mon Nov 24, 2008 1:27 pm
If the operation @ is defined for all integers a and b by a@b=a+b-ab,which of the following statements must be true for all integers a,b and c
I)a@b=b@a
II)a@0=a
III)(a@b)@c =a@(b@c)
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by orel » Mon Nov 24, 2008 10:12 pm
still doesn't make any sense :(
why 27 ?
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Re: Please explain on some GMAT prep1 quant questions

by jimmiejaz » Tue Nov 25, 2008 2:07 am
nothinglessthan780 wrote:Hi folks...I am not able to get the correct answer for the following questions on Gmatprep1..somebody please explain.

1.For all positive integers m,[m] = 3m when m is odd and [m]=1/2m when m is even.Which of the following is equivalent to [9]*[6]
A)81
B)54
C)36
D)27
E)18

Following the given info..i substituted m for 9 and since9 is odd [m] became 3*9 = 27 and m for 6 and since 6 is even it became (1/2)*6=3
therefore [9]*[6]=27*3=81 which is incorrect...
Anyone with an idea why D)27 is the correct answer?

2.Circular gears P and Q start rotating at the same time at constant speeds.Gear P makes 10 revolutions per minute and gear Q makes 40 revolutions per minute.How many seconds after the gears rotating will gear Q have made exactly 6 more revolutions than gear P?
No idea on how to solve this question.The correct given answer is 12.


Do explanations for GMATPrep Tests exist?
Please chk the line in bold in question 1. It says which of the foll is equivalent to , let me rephrase:
Which of the following choices will give you the same value as you get by [9]*[6] = 81, now [27] = 81 , hence the ans is D.

Hope its clear now.
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Re: Please explain on some GMAT prep1 quant questions

by herjari » Tue Nov 25, 2008 4:32 am
jimmiejaz wrote:
nothinglessthan780 wrote:Hi folks...I am not able

Please chk the line in bold in question 1. It says which of the foll is equivalent to , let me rephrase:
Which of the following choices will give you the same value as you get by [9]*[6] = 81, now [27] = 81 , hence the ans is D.

Hope its clear now.
Thank you VERY much for you excellent explanation. I was totally lost with this one!
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Re: GMAT Prep Questions Explanations

by shukla.chandra » Tue Nov 25, 2008 5:43 am
nothinglessthan780 wrote:Hi Feruza,



One more question..

Q.In a certain deck of cards each card has a positive integer written on it.In a multiplication game,a child draws a card and multiplies the integer on the card by the next larger integer.If each possible product is between 15 and 200, then the least and greatest integers on the cards could be?
I would like to have a different approach to this question:
to find the min int: just think of a number whose square is just above 15: thats 4. So if i assume 4 to be answer, 4*5=20 which suits the criteria. again, to cross-verify, 3*4=12 which is less than 15. So the min int is 4.

to find the max int: nearest perfect square to 200 is 196 whose root is 14. 14 cannot be the max int coz 14*15 > 200. Take 13, it satisfies the condition. So 13 is the max integer.

I found this to be quite logical and can give faster result. Any flaw in the approach would be sincerely appreciated!!
Cheers,
Chandra
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by nothinglessthan780 » Wed Nov 26, 2008 3:22 pm
Thanks guys for your explanations on some of the questions i had.
Jimmie, thanks for explaining the [m] problem.Now understood.
Feruza nd Shukla, thanks for explaing the smallest and largest integer question

I still have a number of other questions i kindly request anyone to help me solve the questions.Sorry they are quite a number of questions. :oops:

Q1)2^x-2^x-2=3(2^13).What is the value of x?
A)9
B)11
C)13
D)15
E)17
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by nothinglessthan780 » Wed Nov 26, 2008 3:54 pm
Anyone who can help me solve these questions please!Sorry they are quite a number of questions. :oops:


Q2)
If the operation @ is defined for all integers a and b by a@b=a+b-ab,which of the following statements must be true for all integers a,b and c
I)a@b=b@a
II)a@0=a
III)(a@b)@c =a@(b@c)

Q3)
The function f is defined for all positive integers n by the following rule.f(n) is the number of positive integers each of which is less than n and has no positive factor in common with n other than 1.If p is any prime number than f(p)=

A)p-1
B)p-2
C)(p+1)/2
D)(p-1)/2
E)2

Q4)
The y-intercept of line l is 4.If the slope of l is negative,which of the following couldbe the x intercept of l?
I)-1
II)0
III)6

Q5)
A college admissions officer predicts that 20% of the students who are accepted will not attend the college.According to this prediction,how many students should be accepted to achieve a planned enrollment of x students?

Q6)
For any positive integer n, the length of n is defined as the number of prime factors whose product is n.For example the length of 75 is 3 since 75=3*5*5.How many two digit positive integers have length 6?

Q7)
Two members of a club are to be selected to represent the club at a national meeting.If there are 190 different possible selections of the 2 members,how many members does the club have?

Q8)
The figures given show sales for 5 salespeople.A-450000,B-360000,C-190000,D-210000,E-680000.It was discovered that one of C's sales was incorrectly recorded as A's.After this error was corrected,A's total sales were still higher than C's total sales and the median of the 5 sales totals was 330000.What is the value of incorrectly recorded sale?

Q9)
Working alone, at its own constant rate, a machine seals k cartons in 8 hours and working alone at its own constant rate, a second machine seals k cartons in 4 hours.If the two machines,each working at its own constant rate and for the same period of time together sealed a certain number of cartons,what percentage was sealed by the faster machine?
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