answer correct? 32

This topic has expert replies
Master | Next Rank: 500 Posts
Posts: 484
Joined: 30 Jul 2006
Thanked: 2 times
Followed by:1 members

answer correct? 32

by magical cook » Wed Dec 19, 2007 8:05 am
If n is an integer between 10 and 99, is n < 80 ?
(1) The sum of the two digits of n is a prime number.
(2) Each of the two digits of n is a prime number.




I think B but it says C..

Master | Next Rank: 500 Posts
Posts: 158
Joined: 03 Dec 2007
Thanked: 7 times

by StarDust845 » Wed Dec 19, 2007 8:45 am
well there atleast two numbers 32 and 52.

Calista.

User avatar
Legendary Member
Posts: 986
Joined: 20 Dec 2006
Location: India
Thanked: 51 times
Followed by:1 members

by gabriel » Wed Dec 19, 2007 10:45 am
Hi Magical Cook,

Well, I would say B too, there is no two digit number greater than 80 that has both its integer prime, so n has to be less that 80 .. btw what is the source of the question

Regards

Master | Next Rank: 500 Posts
Posts: 484
Joined: 30 Jul 2006
Thanked: 2 times
Followed by:1 members

by magical cook » Wed Dec 19, 2007 1:42 pm
Hmm. This is from gmatprep. so, answer should be correct but I dont understand why it's C..

Master | Next Rank: 500 Posts
Posts: 460
Joined: 25 Mar 2007
Thanked: 27 times

by samirpandeyit62 » Wed Dec 19, 2007 11:39 pm
I dont see how the ans can be C

If n is an integer between 10 and 99, is n < 80 ?

(2) Each of the two digits of n is a prime number.

for this stmt to be false we need to deduce that both n<80

& n GE (greater than or equal to) 80
are possible

n<80 we have 73

but for n GE (greater than or equal to) 80, we will have values
80-89 (first digit is eight) 90-99 (first digit 9) so none of these numbers would satisfy stmt 2

however is there a possibility that a soln can be incorrect in gmatprep?
Regards
Samir

Legendary Member
Posts: 645
Joined: 05 Sep 2007
Location: India
Thanked: 34 times
Followed by:5 members

by camitava » Thu Dec 20, 2007 12:44 am
Magical_cook, ur Qs is -
If n is an integer between 10 and 99, is n <80> 80
or = 21, 23, ... When n < 80
So not A or D.
If we go by 2,
n = any prime number at unit's digit with 3, 5 and 7 but neither 8 nor 9 as ten's digit .

Now by this, we can conclude by B that the best option to chose is B. Guys am I correct?
Correct me If I am wrong


Regards,

Amitava

Senior | Next Rank: 100 Posts
Posts: 36
Joined: 20 Jul 2010
Thanked: 1 times
Followed by:1 members

by rbansal » Mon May 16, 2011 5:33 pm
magical cook wrote:If n is an integer between 10 and 99, is n < 80 ?
(1) The sum of the two digits of n is a prime number.
(2) Each of the two digits of n is a prime number.


The answer for this is B I have the GMAT Prep answer and it is B.



I think B but it says C..

Newbie | Next Rank: 10 Posts
Posts: 9
Joined: 08 Apr 2011
Thanked: 4 times
GMAT Score:680

by jerseyny » Fri May 20, 2011 7:48 pm
wow if the answer is C it means that I have to study a lot more.. I do think its B?

For example, as Each of the two digit needs to be a prime number and 8 and 9 is not a prime, there couldn't be any number which satisfies this condition if the number is bigger than 80... as there will always be one number which is not prime..

User avatar
Newbie | Next Rank: 10 Posts
Posts: 7
Joined: 22 Feb 2011
Thanked: 1 times

by uslalas22 » Fri May 20, 2011 8:02 pm
Agree as well that it should be B for the reasoning's noted.

Newbie | Next Rank: 10 Posts
Posts: 2
Joined: 10 May 2011

by vineethyoung » Mon Dec 05, 2011 2:21 am
First thing I did was to reframe the question:
10<n<99, is n<80?

For (2) Each of the two digits of n is a prime number:
I listed some #'s that only have prime #'s for each of the two digits, such as, 22, 33, 55, 77, etc. From this I deduced that the largest number n could be is 77, thus n<80. SUFF

For (1) The sum of the two digits of n is a prime number.
This was a little more tedious, I listed all possible combo's in my own short way:
1 1
2 2
3 3
4 4
5 5
6 6
7 7
8 8
9 9

By visualizing this I could use connecting arrows to see what the possibilities are. I could make a combo of a # below 80, such as, if n = 74 -> then 7+4 = 11, a prime number, and thus n<80 (and still maintaining 10<n<99).
Also, I could make a combo of a # greater than 80, such as, if n = 83 -> 8+ 3 = 11, a prime number, and thus n>80. Since we have n<80 and n>80, INSUFF.

Thus answer is B.

User avatar
Master | Next Rank: 500 Posts
Posts: 461
Joined: 10 May 2011
Location: pune
Thanked: 36 times
Followed by:3 members

by amit2k9 » Mon Dec 05, 2011 2:48 am
10< n < 99
if both digits are prime.Then 8 and 9 are ruled out.
hence its B.

If its C then something is missing in the question.
For Understanding Sustainability,Green Businesses and Social Entrepreneurship visit -https://aamthoughts.blogspot.com/
(Featured Best Green Site Worldwide-https://bloggers.com/green/popular/page2)

Junior | Next Rank: 30 Posts
Posts: 10
Joined: 26 Nov 2011
Thanked: 1 times

by anikendra » Tue Dec 06, 2011 9:35 am
answer is B as per the answer in gmatprep...

User avatar
Legendary Member
Posts: 934
Joined: 09 Nov 2010
Location: AAMCHI MUMBAI LOCAL
Thanked: 63 times
Followed by:14 members

by amit.trivedi@ymail.com » Sat Feb 18, 2012 6:22 am
Are you sure Aniket that the answer is B as per the GMAT prep...

though it should be B as we all have solved it but just check all of you guyz once inorder to know wat is the OA...
IT IS TIME TO BEAT THE GMAT

LEARNING, APPLICATION AND TIMING IS THE FACT OF GMAT AND LIFE AS WELL... KEEP PLAYING!!!

Whenever you feel that my post really helped you to learn something new, please press on the 'THANK' button.