a(1), a(2),...., a(15)
In the sequence shown, a(n) = a(n-1) + k, where 2<=n<=15 and k is a nonzero constant. How many of the terms in the sequence are greater than 10?
1) a(1)=24
2) a(8)=10
Can someone help me solve the above problem. OA is B.
Arithmatic sequence
This topic has expert replies
-
- Senior | Next Rank: 100 Posts
- Posts: 85
- Joined: Mon Nov 12, 2012 11:12 am
- Thanked: 8 times
- Followed by:2 members
- GMATGuruNY
- GMAT Instructor
- Posts: 15539
- Joined: Tue May 25, 2010 12:04 pm
- Location: New York, NY
- Thanked: 13060 times
- Followed by:1906 members
- GMAT Score:790
Statement 1 is clearly insufficient.Anindya Madhudor wrote:a(1), a(2),...., a(15)
In the sequence shown, a(n) = a(n-1) + k, where 2<=n<=15 and k is a nonzero constant. How many of the terms in the sequence are greater than 10?
1) a(1)=24
2) a(8)=10
.
Statement 2: a₈ = 10.
If k>0, then the sequence is INCREASING: each term in the sequence is GREATER than the preceding term.
In this case, a₉...a�₅ -- a total of 7 terms -- will be greater than 10.
If k<0, then the sequence is DECREASING: each term in the sequence is LESS than the preceding term.
In this case, a�...a₇ -- a total of 7 terms -- will be greater than 10.
In each case, the number of terms greater than 10 = 7.
SUFFICIENT.
The correct answer is B.
Private tutor exclusively for the GMAT and GRE, with over 20 years of experience.
Followed here and elsewhere by over 1900 test-takers.
I have worked with students based in the US, Australia, Taiwan, China, Tajikistan, Kuwait, Saudi Arabia -- a long list of countries.
My students have been admitted to HBS, CBS, Tuck, Yale, Stern, Fuqua -- a long list of top programs.
As a tutor, I don't simply teach you how I would approach problems.
I unlock the best way for YOU to solve problems.
For more information, please email me (Mitch Hunt) at [email protected].
Student Review #1
Student Review #2
Student Review #3
Followed here and elsewhere by over 1900 test-takers.
I have worked with students based in the US, Australia, Taiwan, China, Tajikistan, Kuwait, Saudi Arabia -- a long list of countries.
My students have been admitted to HBS, CBS, Tuck, Yale, Stern, Fuqua -- a long list of top programs.
As a tutor, I don't simply teach you how I would approach problems.
I unlock the best way for YOU to solve problems.
For more information, please email me (Mitch Hunt) at [email protected].
Student Review #1
Student Review #2
Student Review #3
- nisagl750
- Master | Next Rank: 500 Posts
- Posts: 145
- Joined: Tue Jan 31, 2012 6:50 am
- Location: New Delhi
- Thanked: 16 times
- Followed by:2 members
- GMAT Score:760
S1: Insuff, We don't know K is positive or negative
S2: Suff, If a8 is 10, then either a1, a2, ....a7 (7 terms) will be less than 10 if K>0
or a9,a10,.....a15 (7 terms) will be less than 10 if K<0
Its B
S2: Suff, If a8 is 10, then either a1, a2, ....a7 (7 terms) will be less than 10 if K>0
or a9,a10,.....a15 (7 terms) will be less than 10 if K<0
Its B