Last visit was: 21 May 2024, 04:39 It is currently 21 May 2024, 04:39
Close
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

we will pick new questions that match your level based on your Timer History

Track
Your Progress

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History
Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.
Close
Request Expert Reply
Confirm Cancel
SORT BY:
Date
Tags:
Show Tags
Hide Tags
User avatar
Intern
Intern
Joined: 14 May 2008
Posts: 19
Own Kudos [?]: 777 [29]
Given Kudos: 0
Send PM
Most Helpful Reply
User avatar
Intern
Intern
Joined: 11 Apr 2008
Posts: 47
Own Kudos [?]: 203 [14]
Given Kudos: 0
Location: Chicago
Send PM
Math Expert
Joined: 02 Sep 2009
Posts: 93365
Own Kudos [?]: 625479 [6]
Given Kudos: 81917
Send PM
General Discussion
User avatar
Senior Manager
Senior Manager
Joined: 12 Apr 2008
Posts: 413
Own Kudos [?]: 368 [1]
Given Kudos: 4
Location: Eastern Europe
Schools:Oxford
 Q49  V42
Send PM
Re: In the sequence of nonzero numbers t1, t2, t3, , tn, , tn+1 [#permalink]
1
Kudos
Hello, quantum,
this is my attempt to explain why it's D:

Quote:
In the sequence of nonzero numbers t1, t2, t3, …, tn, …, tn+1 = tn / 2 for all positive integers
n. What is the value of t5?
(1) t3 = 1/4
(2) t1 - t5 = 15/16


Here we have geometric progression, i.e. series where t2=t1*q, t3=t2*q, …, tn+1=tn*q. In our case, q=0.5. Also note that tn+1=t1*q^n

So, basically, to answer this question, it is sufficient to know the value of any of the tn.

1) Explicitly gives us the value for t3, so it’s sufficient.

2) So, let’s see if we can obtain the value of t1 from this statement, using the formula tn+1=t1*q^n:

15/16=t1-t5=t1-t1*q^4 = t1*(1-q^4) = t1*(1-1/16) = t1*15/16.

So, from here it follows that t1=1 and t5=t1*q^4 = 1*1/16 = 1/16.

Sufficient.

I hope that helped.
avatar
Manager
Manager
Joined: 13 Jul 2010
Posts: 81
Own Kudos [?]: 219 [0]
Given Kudos: 7
Send PM
Re: In the sequence of nonzero numbers t1, t2, t3, , tn, , tn+1 [#permalink]
Good explanations but I got confused at how you equated tn+1=tn/2? I thought the it was the entire expression that equaled to tn/2? sorry but I am a bit confused. Thanks.
avatar
Manager
Manager
Joined: 13 Jul 2010
Posts: 81
Own Kudos [?]: 219 [0]
Given Kudos: 7
Send PM
Re: In the sequence of nonzero numbers t1, t2, t3, , tn, , tn+1 [#permalink]
Thanks for the explanation Bunuel. I can see it now clearly.
avatar
Intern
Intern
Joined: 08 Jan 2014
Posts: 16
Own Kudos [?]: 23 [2]
Given Kudos: 4
Location: United States
Concentration: General Management, Entrepreneurship
GMAT Date: 06-30-2014
GPA: 3.99
WE:Analyst (Consulting)
Send PM
Re: In the sequence of nonzero numbers t1, t2, t3, , tn, , tn+1 [#permalink]
2
Kudos
statement(1)

tn+1 = tn/2
t3 = 1/4
t4 =t3/2 = 1/8
t5 = t4/2 = 1/16. Sufficient.

statement (2)
t1 - t5 = 15/16
t1 = t5 + 15/16 = (16t5 + 15) /16
t2 = t1/2 = (16t5 + 15) / 32
t3 = t2/2 = (16t5 + 15) /64
t4 = t3/2 = (16t5 + 15) /128
t5 = t4/2 = (16t5 + 15) /256

256t5 = 16t5 + 15
240t5 = 15
t5 = 15/240 = 5/80 = 1/16
Sufficient.


Thus, D.
Intern
Intern
Joined: 31 Jan 2016
Posts: 14
Own Kudos [?]: 21 [0]
Given Kudos: 6
Send PM
Re: In the sequence of nonzero numbers t1, t2, t3, , tn, , tn+1 [#permalink]
I am having trouble understanding how you went from T3 = T2/2 = T1/4

Please explain
Board of Directors
Joined: 18 Jul 2015
Status:Emory Goizueta Alum
Posts: 3600
Own Kudos [?]: 5435 [1]
Given Kudos: 346
Send PM
Re: In the sequence of nonzero numbers t1, t2, t3, , tn, , tn+1 [#permalink]
1
Kudos
Expert Reply
g3lo18 wrote:
I am having trouble understanding how you went from T3 = T2/2 = T1/4

Please explain


Notice that we are given T(n+1) = T(n)/2

So, substitute n = 2, you will get T(3) = T(2)/2.

Now substitute n =1 , you will get T(2) = T(1)/2

So, we can say T(3) = T(2)/2 = T(1)/4
Intern
Intern
Joined: 31 Jan 2016
Posts: 14
Own Kudos [?]: 21 [0]
Given Kudos: 6
Send PM
Re: In the sequence of nonzero numbers t1, t2, t3, , tn, , tn+1 [#permalink]
OMG I see it now. Thank you. Wow these are so annoying to deal with. Guess I need to get accustomed to it.
User avatar
Non-Human User
Joined: 09 Sep 2013
Posts: 33132
Own Kudos [?]: 828 [0]
Given Kudos: 0
Send PM
Re: In the sequence of nonzero numbers t1, t2, t3, , tn, , tn+1 [#permalink]
Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.
GMAT Club Bot
Re: In the sequence of nonzero numbers t1, t2, t3, , tn, , tn+1 [#permalink]
Moderator:
Math Expert
93365 posts