Events & Promotions
|
|
GMAT Club Daily Prep
Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.
Customized
for You
Track
Your Progress
Practice
Pays
Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.
Apr 2301:30 AM EDT
-02:30 AM EDT
Struggling with GMAT Verbal as a non-native speaker? Harsh improved his score from 595 to 695 in just 45 days—and scored a 99 %ile in Verbal (V88)! Learn how smart strategy, clarity, and guided prep helped him gain 100 points.
Apr 2212:30 AM EDT
-01:30 AM EDT
At one point, she believed GMAT wasn’t for her. After scoring 595, self-doubt crept in and she questioned her potential. But instead of quitting, she made the right strategic changes. The result? A remarkable comeback to 695. Check out how Saakshi did it.
Apr 2308:00 PM PDT
-09:00 PM PDT
Video explanations + diagnosis of 10 weakest areas + 150+ short videos + study plan!
Apr 2610:00 AM EDT
-11:00 AM EDT
The Target Test Prep course represents a quantum leap forward in GMAT preparation, a radical reinterpretation of the way that students should study. Try before you buy with a 5-day, full-access trial of the course for FREE!
Apr 2711:00 AM EDT
-12:00 PM EDT
Prefer video-based learning? The Target Test Prep OnDemand course is a one-of-a-kind video masterclass featuring 400 hours of lecture-style teaching by Scott Woodbury-Stewart, founder of Target Test Prep and one of the most accomplished GMAT instructors
Apr 2808:00 AM PDT
-11:00 AM PDT
Whether you are just beginning your MBA journey or fine-tuning your path to a 700+ score, GMAT Day is designed to give you a competitive edge.
D
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
45%
(medium)
Question Stats:
74% (02:45) correct
26%
(02:55)
wrong
based on 644
sessions
History
Date
Time
Result
Not Attempted Yet
The sequence \(a_1\), \(a_2\), \(a_3\) ... \(a_n\) is defined such that \(a_n=a_{n-1}+9+n\) for all \(n>1\). If \(a_1=10\), what is the value of \(a_{11}\)?
(A) 150
(B) 155
(C) 160
(D) 165
(E) 170
(A) 150
(B) 155
(C) 160
(D) 165
(E) 170
27 Apr 2020, 13:49
Kudos
Bookmarks
\(a_2 = a_1 + 9+2 = a_1+11\)
\(a_3 = a_2+9+3= a_1+11+12\)
\(a_{11}= a_1+11+12+....+(9+11)\)
\(a_{11} = 10+11+12....+20 = \frac{(20+10)}{2} * 11 = 165\)
\(a_3 = a_2+9+3= a_1+11+12\)
\(a_{11}= a_1+11+12+....+(9+11)\)
\(a_{11} = 10+11+12....+20 = \frac{(20+10)}{2} * 11 = 165\)
Ravixxx
KhulanE
24 Feb 2021, 19:25
Kudos
Bookmarks
\(A_n\)=\(A_{n-1}\)+9+n we can convert this formula into this one. -> \(A_n\)-\(A_{n-1}\)=9+n
now we can substitute numbers n to numbers from 1 to 11 just like below one
\(A_{11}\)-\(A_{10}\)=9+11
\(A_{10}\)-\(A_9\)=9+10
\(A_9\)-\(A_8\)=9+9
...
\(A_3\)-\(A_2\)=9+3
\(A_2\)-\(A_1\)=9+2
if you add up above all, all left is below equation
\(A_{11}\)-\(A_1\)=9*10+(2+3+...+11)=90+\(\frac{11*12}{2}\)-1=155
\(A_{11}\)-10=155
\(A_{11}\)=165
if you wonder how this part (2+3+...+11) ended up to this part (\(\frac{11*12}{2}\)-1), refer to the below explanation.
2+3+...+11=(1+2+3+...+11)-1=\(\frac{11*12}{2}\)-1=65
here is the formula of the consecutive integers from 1 to n: sum=\(\frac{n*(n+1)}{2}\)
now we can substitute numbers n to numbers from 1 to 11 just like below one
\(A_{11}\)-\(A_{10}\)=9+11
\(A_{10}\)-\(A_9\)=9+10
\(A_9\)-\(A_8\)=9+9
...
\(A_3\)-\(A_2\)=9+3
\(A_2\)-\(A_1\)=9+2
if you add up above all, all left is below equation
\(A_{11}\)-\(A_1\)=9*10+(2+3+...+11)=90+\(\frac{11*12}{2}\)-1=155
\(A_{11}\)-10=155
\(A_{11}\)=165
if you wonder how this part (2+3+...+11) ended up to this part (\(\frac{11*12}{2}\)-1), refer to the below explanation.
2+3+...+11=(1+2+3+...+11)-1=\(\frac{11*12}{2}\)-1=65
here is the formula of the consecutive integers from 1 to n: sum=\(\frac{n*(n+1)}{2}\)
