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OG PS #171 - Easy Sequence Question!

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This topic has 1 expert reply and 3 member replies
kalifalk Newbie | Next Rank: 10 Posts
Joined
25 Nov 2009
Posted:
4 messages

OG PS #171 - Easy Sequence Question!

Thu Dec 15, 2011 8:01 am
Hello all,

I've never posted before, but I have a simple question about OG PS question #171. Question is:

"What is the difference between the sixth and the fifth terms of the sequence 2, 4, 7.... whose nth term is n+2^n-1."

According to the answer, you simply plug 6 and 5 into the term formula, but my question is why did they list seemingly random numbers first... I had assumed that those were the 1st, 2nd, and 3rd terms, I tried to plug them in as recursive numbers.

If someone could explain that would be fantastic

Thanks guys! Happy studying and/or happy tutoring!

Kali

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GMAT/MBA Expert

Jeff@TargetTestPrep GMAT Instructor
Joined
09 Apr 2015
Posted:
506 messages
Followed by:
6 members
39
Fri Jul 10, 2015 4:36 am
kalifalk wrote:
Hello all,

I've never posted before, but I have a simple question about OG PS question #171. Question is:

"What is the difference between the sixth and the fifth terms of the sequence 2, 4, 7.... whose nth term is n+2^n-1."

According to the answer, you simply plug 6 and 5 into the term formula, but my question is why did they list seemingly random numbers first... I had assumed that those were the 1st, 2nd, and 3rd terms, I tried to plug them in as recursive numbers.

If someone could explain that would be fantastic

Thanks guys! Happy studying and/or happy tutoring!

Kali
What is the difference between the sixth and the fifth terms of the sequence 2, 4, 7, ... whose nth term is n + 2^(n - 1)?

(A) 2
(B) 3
(C) 6
(D) 16
(E) 17

Solution:

To find the sixth term, let's first substitute 6 for n.

6 + 2^(6-1)

6 + 2^5

6 + 32 = 38

To find the fifth term, we substitute 5 for n.

5 + 2^(5-1)

5 + 2^4

5 + 16 = 21

The difference between the 6th and 5th terms of the sequence is 38 - 21 = 17.

_________________
Jeffrey Miller Head of GMAT Instruction

greatsaint Junior | Next Rank: 30 Posts
Joined
18 Mar 2009
Posted:
16 messages
Sat Apr 28, 2012 5:37 am
kalifalk wrote:
Hello all,

I've never posted before, but I have a simple question about OG PS question #171. Question is:

"What is the difference between the sixth and the fifth terms of the sequence 2, 4, 7.... whose nth term is n+2^n-1."

According to the answer, you simply plug 6 and 5 into the term formula, but my question is why did they list seemingly random numbers first... I had assumed that those were the 1st, 2nd, and 3rd terms, I tried to plug them in as recursive numbers.

If someone could explain that would be fantastic

Thanks guys! Happy studying and/or happy tutoring!

Kali
The first term in the sequnce is n=0. So for the 5th term, n=4 and 6th term , n=5.
Thus your answer comes to (4+2)^(4-1) which 6^3 and the 6th term should be (5+2)^(5-1) which is 7^4.

Here, as you notice value of n is 1 less than the term of the sequnce (Eg: Sixth term is n=5). I feel this is the trick that they are testing.

GMAT/MBA Expert

Jeff@TargetTestPrep GMAT Instructor
Joined
09 Apr 2015
Posted:
506 messages
Followed by:
6 members
39
Fri Jul 10, 2015 4:36 am
kalifalk wrote:
Hello all,

I've never posted before, but I have a simple question about OG PS question #171. Question is:

"What is the difference between the sixth and the fifth terms of the sequence 2, 4, 7.... whose nth term is n+2^n-1."

According to the answer, you simply plug 6 and 5 into the term formula, but my question is why did they list seemingly random numbers first... I had assumed that those were the 1st, 2nd, and 3rd terms, I tried to plug them in as recursive numbers.

If someone could explain that would be fantastic

Thanks guys! Happy studying and/or happy tutoring!

Kali
What is the difference between the sixth and the fifth terms of the sequence 2, 4, 7, ... whose nth term is n + 2^(n - 1)?

(A) 2
(B) 3
(C) 6
(D) 16
(E) 17

Solution:

To find the sixth term, let's first substitute 6 for n.

6 + 2^(6-1)

6 + 2^5

6 + 32 = 38

To find the fifth term, we substitute 5 for n.

5 + 2^(5-1)

5 + 2^4

5 + 16 = 21

The difference between the 6th and 5th terms of the sequence is 38 - 21 = 17.

_________________
Jeffrey Miller Head of GMAT Instruction

greatsaint Junior | Next Rank: 30 Posts
Joined
18 Mar 2009
Posted:
16 messages
Sat Apr 28, 2012 5:37 am
kalifalk wrote:
Hello all,

I've never posted before, but I have a simple question about OG PS question #171. Question is:

"What is the difference between the sixth and the fifth terms of the sequence 2, 4, 7.... whose nth term is n+2^n-1."

According to the answer, you simply plug 6 and 5 into the term formula, but my question is why did they list seemingly random numbers first... I had assumed that those were the 1st, 2nd, and 3rd terms, I tried to plug them in as recursive numbers.

If someone could explain that would be fantastic

Thanks guys! Happy studying and/or happy tutoring!

Kali
The first term in the sequnce is n=0. So for the 5th term, n=4 and 6th term , n=5.
Thus your answer comes to (4+2)^(4-1) which 6^3 and the 6th term should be (5+2)^(5-1) which is 7^4.

Here, as you notice value of n is 1 less than the term of the sequnce (Eg: Sixth term is n=5). I feel this is the trick that they are testing.

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