View Full Version : solve this one

swethav12

12-06-2004, 09:47 PM

Given an integer C , how many integers are greater than C and less than 2C

C/2

C

C-1

C-2

C+1

4.How many positive integers less than 20 are equal to the sum of a positive multiple of 3 and a positive multiple of 4?

(A) Two (B) Five (C) Seven (D) Ten (E) Nineteen

3. C-1

2C-C= C

C-1 because you don't count integers C & 2C.

swethav12

12-06-2004, 10:56 PM

http://www.downdowndown.net/images/gremath_05.gif

http://www.downdowndown.net/images/gremath_06.gif

7.In 1984 median income for a person in the 55-64 age category was in which of the following intervals?

(A) less than $10,000 (B) $10,000-$19,999 (C) $20,000-$24,999

(D) $25,000-$34,999 (E) $35,000-$49,999

swethav12

12-07-2004, 06:55 PM

hi can any one explain me the above median problem is the answer C for this problem

gaurava

12-07-2004, 07:04 PM

Given an integer C , how many integers are greater than C and less than 2C

C/2

C

C-1

C-2

C+1

4.How many positive integers less than 20 are equal to the sum of a positive multiple of 3 and a positive multiple of 4?

(A) Two (B) Five (C) Seven (D) Ten (E) Nineteen

1. C-1 only if C>=1

2. 10 (Brute force - any analytical solutions??)

gaurava

12-07-2004, 07:07 PM

hi can any one explain me the above median problem is the answer C for this problem

Yes C should be the answer. I guess we just need to look at 50% line where it crosses the bar.

swethav12

12-07-2004, 07:11 PM

Hi gaurav how did u get answer as 10 for the second Q

do u have any idea regarding the median problem

gaurava

12-07-2004, 07:28 PM

Hi gaurav how did u get answer as 10 for the second Q

do u have any idea regarding the median problem

I used brute force. Just list down all numbers from 1-20. Then cross-off numbers that can be created in the form 3a+4b with a,b>0. Obviously 1-6 can not be written in this form. Other nos that can not be written in this form were 8,9,12,20.

I would appreciate an analytical solution though.

I already answered on median. To calculate median, you need to sort the available data and pick the middle one (in loose sense). The second chart already shows ascending data in bar-graph so just pick the middle one (50%).

adonis

12-07-2004, 07:56 PM

4.How many positive integers less than 20 are equal to the sum of a positive multiple of 3 and a positive multiple of 4?

(A) Two (B) Five (C) Seven (D) Ten (E) Nineteen

(1) pos. mult. of 3

3

6

9

12

15

(2) positive multiples of 4

4

8

12

16

Now consider the first multiple of 4, i.e 4 . The numbers of multiples it can combine with in column 1 to give a sum less than 20 is 5 ( 3+4 , 6+4, 9+4, 12+4, 15 + 4). Similarly we have 3 for eight, 2 for 12 and 1 for 16.

Adding all these( 5,3,2,1) we have 11.

But the sum of (3 + 16) and (4+15) give u the same result 19 which is counted twice. The question is " positive integers less than 20". Therefore, we get 11-1 = 10.

Cheers

adonis

What's the answer for #1. 3? Did I get it right? Guarava, the point here is to choose one choice for the right ans. You're ans. isn't even one of the choices. Although it is admirable that you are pointing out the intracies of question, please don't waste people's time with overanalyzing and making the problem more complex than it actually is. Most people are here to do well on the GRE and have limited time schedules to study for the exam. They're not here to take a math course.

gaurava

12-07-2004, 08:12 PM

What's the answer for #1. 3? Did I get it right? Guarava, the point here is to choose one choice for the right ans. You're ans. isn't even one of the choices. Although it is admirable that you are pointing out the intracies of question, please don't waste people's time with overanalyzing and making the problem more complex than it actually is. Most people are here to do well on the GRE and have limited time schedules to study for the exam. They're not here to take a math course.

Ok thanks. I understand that. Yes, your answer was the best out of given choices. BTW, it was not an overanalysis. The question had a deficiency and I just pointed it out. ETS frames questions much carefully and such type of problems should not be there in real exam.

adonis

12-07-2004, 08:14 PM

Given an integer C , how many integers are greater than C and less than 2C

C/2

C

C-1

C-2

C+1

777 u're rite.

"Not between"

Gaurava, if u consider C to be a negative number, 2C will be a number smaller than C. ( - 4 < - 2) So u'll end up having zero as the answer as the two sets are non overlapping.

Please read the question thoroughly b4 u try and give a solution. There are a lotta ppl. who wanna learn a few things here. Don't confuse them. Take it as a friendly advice. Plz don't be offended.

Cheers

adonis

gaurava

12-07-2004, 08:19 PM

777 u're rite.

Gaurava, if u consider C to be a negative number, 2C will be a number smaller than C. ( - 4 < - 2) So u'll end up having infinite as the answer coz greater than C u'll have all those numbers from C extending into positive integers to infinity and less than 2C u'll have integers extending upto minus infinity.

Please read the question thoroughly b4 u try and give a solution. There are a lotta ppl. who wanna learn a few things here. Don't confuse them. Take it as a friendly advice. Plz don't be offended.

Cheers

adonis

My apologies if I confused anyone.

BTW, if you consider negative numbers, answer will be zero because both the sets that you described are non-overlapping. The "and" in the question, I believe, is intersection operation and not union operation.

adonis

12-07-2004, 08:23 PM

u seem to amaze me nontheless. missed the and. Is this wat they call "a taste of ur own medicine"?

u r rite Gaurava. u mus' be in sum kinduva advanced math forum. :-)

Promptly edited my previous post.

Cheers

adonis

Big Dog 04

12-08-2004, 12:50 AM

3.To the median question I thought the answer is B. Doesnt the 50% mark go downwards thus correspond to the $10000 mark on the 55-64 age group? otherwise what are the point of those lines??

1. I tried this also came up with the flawed c-1. Does anyone know the correct answer?

2. also got 10- dont know a shortcut for it unfortunately.

bujji

12-08-2004, 02:17 AM

Thank you for posting the median problem Swetav,I was stuck while doing it this morning. Now I got it !!

adonis

12-08-2004, 05:50 AM

1. I tried this also came up with the flawed c-1. Does anyone know the correct answer?

2. also got 10- dont know a shortcut for it unfortunately.

c-1 is the answer big dog. It certainly is not flawed.

As for 2 did u check out the post that i made earlier in this forum. Hope it helps.

Cheers

adonis

bigduke

12-08-2004, 07:03 AM

Hmm! ok i got the median one incorrect adonis but got the other two correct (kept getting the count as 11, was counting 19 twice :D so i picked the closest answer). That graph is specious I tell you ... the GRE is evil .... all evil :D