integers

Expert replies

Previous Topic Next Topic

vscid: Master | Next Rank: 500 Posts; Posts: 212; Joined: Sat Dec 01, 2007 4:19 pm; Thanked: 5 times

by vscid » Sun Dec 21, 2008 7:34 am

If A and B are integers, is B even?

1] 3a + 4b is even
2] 3a + 5b is even

The GMAT is indeed adaptable. Whenever I answer RC, it proficiently 'adapts' itself to mark my 'right' answer 'wrong'.

Like this post

Source: Beat The GMAT — Data Sufficiency | Sun Dec 21, 2008 7:34 am

ronniecoleman: Legendary Member; Posts: 546; Joined: Sun Nov 16, 2008 11:00 pm; Location: New Delhi , India; Thanked: 13 times

by ronniecoleman » Sun Dec 21, 2008 7:42 am

] 3a + 4b is even
b can be anything odd or even...

Insuff

2] 3a + 5b is eve

a is even so b has to be even
a is odd so b has to be odd

Hence insuff

together

a is even so b has to be ODD

SO

IMO C

Admission champion, Hauz khaz
011-27565856

Like this post

iamcste: Legendary Member; Posts: 940; Joined: Tue Aug 26, 2008 3:22 amFollowed by: 1 member; Thanked: 55 times

by iamcste » Sun Dec 21, 2008 8:34 am

ronniecoleman wrote:]
together

a is even so b has to be ODD

SO

IMO C

As per your conclusions,
a=Even =assume 2 , b=Odd=1

3a+4b=10
3a+5b=11

Contradicts the facts given

so, even though Ans is C, Conclusions are incorrect IMO

Combining equations "3a+4b" and "3a+5b" are even only when both a and b are even and not when B is odd as you mentioned.

Pls let me know if I have missed anything

Like this post

ronniecoleman: Legendary Member; Posts: 546; Joined: Sun Nov 16, 2008 11:00 pm; Location: New Delhi , India; Thanked: 13 times

by ronniecoleman » Sun Dec 21, 2008 9:10 am

iamcste wrote:
ronniecoleman wrote:]
together

a is even so b has to be ODD

SO

IMO C
As per your conclusions,
a=Even =assume 2 , b=Odd=1

3a+4b=10
3a+5b=11

Contradicts the facts given

so, even though Ans is C, Conclusions are incorrect IMO

Combining equations "3a+4b" and "3a+5b" are even only when both a and b are even and not when B is odd as you mentioned.

Pls let me know if I have missed anything

when combining both the statments i need to take the value of A that satisfies both the equation...

3a+ 4b
now 4b is always even
3a has to be even for its sum to be even
so a has to be even...
because ODD*ODD = ODD

3a+ 5b

now it can odd + odd
even + even

3a = a can be odd or even but common solution suggest a has to be even

now 3( even) + 5 ( even) for its sum to be even

Admission champion, Hauz khaz
011-27565856

Like this post

iamcste: Legendary Member; Posts: 940; Joined: Tue Aug 26, 2008 3:22 amFollowed by: 1 member; Thanked: 55 times

by iamcste » Sun Dec 21, 2008 9:20 am

ronniecoleman wrote:
iamcste wrote:
ronniecoleman wrote:]
together

a is even so b has to be ODD

SO

IMO C
As per your conclusions,
a=Even =assume 2 , b=Odd=1

3a+4b=10
3a+5b=11

Contradicts the facts given

so, even though Ans is C, Conclusions are incorrect IMO

Combining equations "3a+4b" and "3a+5b" are even only when both a and b are even and not when B is odd as you mentioned.

Pls let me know if I have missed anything

when combining both the statments i need to take the value of A that satisfies both the equation...

3a+ 4b
now 4b is always even
3a has to be even for its sum to be even
so a has to be even...
because ODD*ODD = ODD

3a+ 5b

now it can odd + odd
even + even

3a = a can be odd or even but common solution suggest a has to be even

now 3( even) + 5 ( even) for its sum to be even

Do you mean "3a = a can be odd or even but common solution suggest b has to be even

If yes, thats what I meant "b" has to be even unlike said in your earlier post "B has to be odd"

Like this post

cramya: Legendary Member; Posts: 2467; Joined: Thu Aug 28, 2008 6:14 pmFollowed by: 11 members; Thanked: 331 times

by cramya » Sun Dec 21, 2008 12:40 pm

Stmt I

3a + 4b -> even (odd+odd->even or even+even->even)

3a-> odd 4b->odd or 3a->even 4b->even

4b can never be odd so 4b has to be even but b could be odd or even

For 3a to be even a has to be even

From stmt I all we know for sure is a is even . b can be odd or even

INSUFF

Stmt II

3a + 5b is even

3a-> odd 4b->odd or 3a->even 5b->even

a and b are bpth odd or both even

INSUFF

Stmt I and II

a is even

3a+4b->even

4b = even-3a

even - 3a is always evene so for 4 b to be even b could be odd or even

3a+5b->even

5b = even-3a

even-3a is always even so 5b has to be even and therefore b has to be even since 5* b(odd) will be odd

B IS EVEN

Choose C)
Whats the OA?

Like this post

vittalgmat: Legendary Member; Posts: 621; Joined: Wed Apr 09, 2008 7:13 pmFollowed by: 4 members; Thanked: 33 times

by vittalgmat » Mon Dec 22, 2008 2:55 am

Excellent explanation Cramya,
I cant add anything to this..
Got C and used the same logic.

Like this post

theprophet: Newbie | Next Rank: 10 Posts; Posts: 2; Joined: Sat May 15, 2010 11:34 pm

by theprophet » Mon Aug 23, 2010 12:03 am

If you consider both together, the simplest way to do it is
3a + 5b is even 3a + 4b is even, if you subtract even from even you get even
which 3a + 5b - 3a - 4b = b which is even.

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