Interesting GMATFix Problem-46

Expert replies

arora007: Community Manager; Posts: 1048; Joined: Mon Aug 17, 2009 3:26 amFollowed by: 27 members; Location: India; Thanked: 51 times; GMAT Score:670

by arora007 » Mon Oct 04, 2010 4:21 am

x and y are positive odd integer. What is the remainder when the product of xy is divided by 18?
1)When x is divided by 9, the remainder is 3
2) y-1 is a multiple of 6

https://www.skiponemeal.org/
https://twitter.com/skiponemeal
Few things are impossible to diligence & skill.Great works are performed not by strength,but by perseverance

pm me if you find junk/spam/abusive language, Lets keep our community clean!!

Like this post

Source: Beat The GMAT — Data Sufficiency | Mon Oct 04, 2010 4:21 am

goyalsau: Legendary Member; Posts: 866; Joined: Mon Aug 02, 2010 6:46 pm; Location: Gwalior, India; Thanked: 31 times

by goyalsau » Mon Oct 04, 2010 4:32 am

I think it should be E,
Am i correct?

Saurabh Goyal
[email protected]
-------------------------

EveryBody Wants to Win But Nobody wants to prepare for Win.

Like this post

selango: Legendary Member; Posts: 1460; Joined: Tue Dec 29, 2009 1:28 amFollowed by: 7 members; Thanked: 135 times

by selango » Mon Oct 04, 2010 5:16 am

Clearly stmt1 and stmt2 alone not sufficient.

combining 1 and 2,

x=9a+3 (21,39,57,75...)

y-1=6b

y=6b+1 (7,13,19,25)

watever the combination we try the remainder is 3.

Pick C

--Anand--

Like this post

okletsdothis: Junior | Next Rank: 30 Posts; Posts: 27; Joined: Fri Aug 13, 2010 8:13 am; GMAT Score:650

by okletsdothis » Mon Oct 04, 2010 9:52 am

how did u get 3 ? and what is the answer here...pls always put the OA with your question.

Like this post

blaster: Master | Next Rank: 500 Posts; Posts: 233; Joined: Mon Jun 09, 2008 1:30 am; Thanked: 5 times

by blaster » Tue Oct 05, 2010 1:30 am

i don't think that answer should be 3 (it must be whether 2 or 4)

but my pick is C

Like this post

mj78ind: Master | Next Rank: 500 Posts; Posts: 265; Joined: Mon Dec 28, 2009 9:45 pmFollowed by: 2 members; Thanked: 26 times; GMAT Score:760

by mj78ind » Tue Oct 05, 2010 4:54 am

selango wrote:Clearly stmt1 and stmt2 alone not sufficient.

combining 1 and 2,

x=9a+3 (21,39,57,75...)

y-1=6b

y=6b+1 (7,13,19,25)

watever the combination we try the remainder is 3.

Pick C

It is ironic that your approach gives me an idea which proves the answer you suggest is correct but the reasoning presented by you is slightly off (I had solved it using brute force and come to C as well!)

x*y = (9a+3)*(6b+1) = 54a + 18b+9a + 3

When we divide this by 18, we get 0 remainders from the first two terms. As we know a is odd, let a = 2p+1 then the last two terms become 9*(2p+1) + 3 when divided by 18 this will always leave a remainder 12

Hence C

Call me 1 - (412) 897 6727 (US) or leave a msg on BTG for GMAT advise / questions.
If you like the solution, check out my debrief at and leave a comment:
https://www.beatthegmat.com/760-done-dea ... 66740.html

Like this post

reply2spg: Legendary Member; Posts: 1261; Joined: Sun Sep 14, 2008 3:46 am; Thanked: 27 times; GMAT Score:570

by reply2spg » Tue Oct 05, 2010 6:05 am

C is correct.

x = {21, 39, 57}
y = {7, 13, 19}

you will always get remainder 1 whenever you divide xy by 18.

Sudhanshu
(have lot of things to learn from all of you)

Like this post

arora007: Community Manager; Posts: 1048; Joined: Mon Aug 17, 2009 3:26 amFollowed by: 27 members; Location: India; Thanked: 51 times; GMAT Score:670

by arora007 » Tue Oct 05, 2010 6:30 am

OA is C

Like this post

anantbhatia: Senior | Next Rank: 100 Posts; Posts: 98; Joined: Sat Feb 06, 2010 11:56 pm; Thanked: 5 times

by anantbhatia » Tue Oct 05, 2010 8:30 am

As we know a is odd, let a = 2p+1

@MJ

why have you assumed a as odd?

Like this post

selango: Legendary Member; Posts: 1460; Joined: Tue Dec 29, 2009 1:28 amFollowed by: 7 members; Thanked: 135 times

by selango » Tue Oct 05, 2010 8:45 am

anantbhatia wrote:
As we know a is odd, let a = 2p+1
@MJ

why have you assumed a as odd?

x=9a+3

Given X is odd.So a must be even in order for X to be odd.

So a=2p

Last 2 terms=18p+3[p=1,2...]

Sub any values of p u ll get remainder as 3

--Anand--

Like this post

anantbhatia: Senior | Next Rank: 100 Posts; Posts: 98; Joined: Sat Feb 06, 2010 11:56 pm; Thanked: 5 times

by anantbhatia » Tue Oct 05, 2010 9:02 am

missed out reading tht x, y are odd.

Like this post

pharmxanthan: Senior | Next Rank: 100 Posts; Posts: 77; Joined: Fri Jan 08, 2010 7:55 am; Thanked: 2 times; GMAT Score:700

by pharmxanthan » Tue Oct 05, 2010 9:55 am

mj78ind wrote:
selango wrote:Clearly stmt1 and stmt2 alone not sufficient.

combining 1 and 2,

x=9a+3 (21,39,57,75...)

y-1=6b

y=6b+1 (7,13,19,25)

watever the combination we try the remainder is 3.

Pick C
It is ironic that your approach gives me an idea which proves the answer you suggest is correct but the reasoning presented by you is slightly off (I had solved it using brute force and come to C as well!)

x*y = (9a+3)*(6b+1) = 54a + 18b+9a + 3

When we divide this by 18, we get 0 remainders from the first two terms. As we know a is odd, let a = 2p+1 then the last two terms become 9*(2p+1) + 3 when divided by 18 this will always leave a remainder 12

Hence C

if we pick numbers, we ger remainder 1 when xy is divided by 18.?

Like this post

[email protected]: Junior | Next Rank: 30 Posts; Posts: 10; Joined: Wed Aug 04, 2010 6:55 am

by [email protected] » Sat Oct 16, 2010 1:52 am

Hi..
Why cant the values of X be 12,21,30,39 and so on...

So considering this..
X=12,21,30,39....
Y=7,13,19,25 and so on...
Case 1:
xy ie. when x=12 and y =7
SO XY =84 and wen divided by 18 the remninder is 12

Case 2: x=21 and y =7
xy= 147 and wen divided by 18 the reminder is 3.
Pls help.
hz do i answer this.

Like this post

[email protected]: Junior | Next Rank: 30 Posts; Posts: 10; Joined: Wed Aug 04, 2010 6:55 am

by [email protected] » Sat Oct 16, 2010 1:54 am

oops sorry sorry.. mistake.. i got it.. oits oly odd positive integers.. ahh..

Like this post

Post new topic Post Reply

• Page 1 of 1

GMAT Course Reviews

560 reviews

1168 reviews

431 reviews

359 reviews

147 reviews

5/5

5 Star (560 Reviews)

"Target Test Prep is the closest to the official version of the GMAT exam, about 99% accuracy in terms of the quality and quantity of information. The course has excellently created singular sets of focused lessons and tests for every possible topic that one could come across in the official GMAT exam."

"The TTP course maximizes the efficiency of the time you spend studying. It will take time and effort but I could almost guarantee that if you complete the course exactly as it is laid out you will get an amazing score. They also have a very responsive team willing to help with any questions you might have."

"TTP has two things that I think no other test prep company offers: A teaching approach that reinforces understanding and an attitude that will give you the mental preparedness needed to succeed on the test. TTP gives you a deep understanding of the concept you need to know while teaching you how to think."

Write a Review