BREAKING: Target Test Prep releases Brand New 2026 On Demand GMAT prep course

Redeem

GMAT Past Paper Test - Algebra

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
Senior | Next Rank: 100 Posts
Posts: 91
Joined: Tue May 01, 2007 4:04 pm

GMAT Past Paper Test - Algebra

by Nisha1218 » Sun Aug 12, 2007 4:34 pm
Can anyone help with the answer to the following question:

If x is an integer and y = 3x + 2, which of the following CANNOT be a divisor of y?

a. 4
b. 5
c. 6
d. 7
e. 8

The answer is C and paper test does not offer explanations. Can someone explain why the answer is C? Thnx!
Top
Source: — Problem Solving |
Master | Next Rank: 500 Posts
Posts: 214
Joined: Fri Jul 20, 2007 1:35 am
Thanked: 3 times

by beny » Sun Aug 12, 2007 6:26 pm
You are increasing in increments of 3:

5, 8, 11, 14, ...

Every 2 increments is an increment of 6. Because the first and second terms are not divisible by 6, the entire sequence will never be divisible by 6.
Top
Senior | Next Rank: 100 Posts
Posts: 91
Joined: Tue May 01, 2007 4:04 pm

by Nisha1218 » Sun Aug 12, 2007 6:56 pm
Thanks Beny!

In your response, what do you mean by the first and second termm (3x??)?
Top
Master | Next Rank: 500 Posts
Posts: 214
Joined: Fri Jul 20, 2007 1:35 am
Thanked: 3 times

by beny » Sun Aug 12, 2007 11:17 pm
The first term is 5 (x=1) and the second term is 8 (x=2).

If the sequence increases by multiples of 3, one of the first two terms must be divisible by 6 or else the entire sequence never will.

I.e.

3, 6, 9, 12

6, 9, 12, 15

9, 12, 15, 18

Clearly every other term would also be a multiple of 6 (since it's increasing by 6 every 2 increments). From the sequence given, you can quickly see no term will ever be divisible by 6.
Top
Senior | Next Rank: 100 Posts
Posts: 91
Joined: Tue May 01, 2007 4:04 pm

by Nisha1218 » Mon Aug 13, 2007 9:13 am
Thanks Beny! Now I fully understand.
Top
Legendary Member
Posts: 1018
Joined: Tue Dec 12, 2006 7:19 pm
Thanked: 86 times
Followed by:6 members

by mayonnai5e » Mon Sep 10, 2007 1:21 pm
There's another explanation:

The equation for any number represented by a quotient, divisor and remainder is:

Y = Xq + r where q is the quotient and r is the remainder

for example: 8/3 = (3)2 + 2

y = 3x + 2 fits this equation perfectly. In other words y divided x has a quotient of 3 and a remainder of 2. What does this tell you? Y is not divisible by 3. If Y is not divisible by 3, it cannot be divisible by 6. So the answer is C.

This explanation is more complicated, but the ideas behind it help in more advanced number property type questions.
Top
Master | Next Rank: 500 Posts
Posts: 460
Joined: Sun Mar 25, 2007 7:42 am
Thanked: 27 times

by samirpandeyit62 » Mon Sep 10, 2007 11:21 pm
If x is an integer and y = 3x + 2, which of the following CANNOT be a divisor of y?

we have y = 3x +2

now 3x is a multiple of 3 hence divisible by 3

so 3x+2 will be 2 greater than 3x i.e 3x+2, hence not divisible by 3

so that means any nos having prime factor as 3 is the ans as it would not divide 3x +2

In the answer choices only 6 = 3 * 2 has 3 as a prime factor

so ans is C
Regards
Samir
Top
Post new topic Post Reply
• Page 1 of 1