Find all School-related info fast with the new School-Specific MBA Forum

 It is currently 30 Mar 2015, 06:13

### GMAT Club Daily Prep

#### Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

# Events & Promotions

###### Events & Promotions in June
Open Detailed Calendar

# I did read the explanations in the book, but I still do not

Author Message
TAGS:
Manager
Joined: 17 Jul 2006
Posts: 50
Followers: 0

Kudos [?]: 4 [0], given: 0

I did read the explanations in the book, but I still do not [#permalink]  02 Jan 2007, 16:02
I did read the explanations in the book, but I still do not get it!!!!!

207)
If n=4p, where p is a prime number greater than 2, how many different positive even divisors does n have, including n?

a)2
b)3
c)4
d)6
e)8

228)
If a two-digit positive integer has its digits reversed, the resulting differs from the original by 27. By how much do the two digits differ?

a)3
b)4
c)5
d)6
e)7

248)
Right triangle PQR is be be constructed in the xy-plane so that the right angle is a P and PR is parallel to the x-axis. The x-and y-coordinates of P, Q, and R are to be integers that satisfy the inequalities -4<x<5 and 6<y<16. How many different triangles with these properties could be constructed?

a)110
b)1100
c)9900
d)10,000
e)12,100
Senior Manager
Joined: 23 Jun 2006
Posts: 387
Followers: 1

Kudos [?]: 310 [0], given: 0

207)
4p has 2 and 4 as its only positive even factors.

228)
check for example 3 and 6 (63-36=27), or any other combination...

248)

i guess you meant -4<=x<=5 and 6<=y<=16 (otherwise none of the answers is correct)...

choosing P's coordinates, there are no constraints so we can choose x freely (10 options) and y freely (11 options)... so we can choose P in 110 options.
now R must have the same y value as P (since it PR is parallel to x-axis).. so we can choose any y except the y value of P (10 options).
Q must be with with the same x as P (to keep the right angle). so it has 9 options for y value.
total is 110*10*9 = 9900
Manager
Joined: 04 Nov 2006
Posts: 158
Followers: 3

Kudos [?]: 8 [0], given: 0

- For #207, any prime greater than 2 has no even divisors, since 2 is the only even prime integer.

Since we're dealing with 4*p and we know p has no even divisors, just focus on the four. 4 obviously has two even divisors, 2 and 4.

- For #228, the question stem tells you that ab - ba = 27. You can reconstruct this as:

(10a + b) - (10b + a) = 27; since ab is just 10a + b and ba is 10b+ a

combining like terms, we get:
9a - 9b = 27

9 (a - b) = 27
a - b = 3
Director
Joined: 24 Aug 2006
Posts: 754
Location: Dallas, Texas
Followers: 5

Kudos [?]: 41 [0], given: 0

Question :
If n=4p, where p is a prime number greater than 2, how many different positive even divisors does n have, including n?

n = 2 ^2 * P

Therefore total number of factors = (2+1) * (1+2) = 6
Now p is a prime factor (other than 2) and not even and 1 is not even.
So total number of evem factors/divisiors = (6-2)=4

_________________

"Education is what remains when one has forgotten everything he learned in school."

Senior Manager
Joined: 23 Jun 2006
Posts: 387
Followers: 1

Kudos [?]: 310 [0], given: 0

re 207...
you caught me off guard here....

you are correct - answer is 4.

cheers....
Senior Manager
Joined: 24 Nov 2006
Posts: 351
Followers: 1

Kudos [?]: 14 [0], given: 0

Re: Questions from OG11 [#permalink]  03 Jan 2007, 11:54
LetÂ´s see.

207) Even factors of 4*p: 2, 2*p, 4, 4*p => C.

208) Let n = ab = 10a + b be the original number. Then (10a + b) - (10b + a) = 9*(a - b) = 27 => a - b = 3 => A.

248) There are (10 + 9 + 8 + ... + 1) * (16 - 6) different triangles with R on (5,6), P to the left of R, and Q above P. There are (10 + 9 + 8 + ... + 1) * (16 - 7) different triangles with R on (5,7) (same reqs as before for P and Q). Iterating: Total number of triangles = (10 * 11 / 2) * (9 * 10 / 2) * 4 = 9900.
Re: Questions from OG11   [#permalink] 03 Jan 2007, 11:54
Similar topics Replies Last post
Similar
Topics:
8 would you still read the explanation? 12 11 Mar 2013, 14:46
Did I do the right thing? 5 04 Oct 2007, 17:54
I still do not get this one! 2 02 Oct 2007, 13:41
This one is from the OG - I read thru the explanation, but 1 14 Sep 2006, 19:45
I did not fully agree with the explanation given for this 3 12 Dec 2005, 20:22
Display posts from previous: Sort by