if the term series is given is given and no condition is

Question

if the term series is given is given and no condition is given, is it ok to assume that all the terms follow the same general formula?

what should be the ans here?

kman · Answer

(1) alone doesn't tell us what Xi could be. It just tells us that each subsequent is half of the previous one
 e.g. Xi could be any number

(2) just gives us the relation between X4 and X5.

When we combine the two, we get

X5 = X4/2 = X4/X4+1

==> X4 + 1 = 2
==> X4 = 1

X5 = .5
X4 = 1
X3 = 2
X2 = 4
X1 = 8

Looks like C

arjtryarjtry · Answer

but on combining the two, THE QUESTION NEVER TELLS US X1. it just tells ,x>1. so how do u get x1?

kman · Answer

From (1) X5 = X4/2
From (2) X5 = X4/X4+1

So, I equated denominators. And problem says formula in (1) valid for i>1, but question stem says sequence starts with X1. After finding X5, I went backwards to find X1. Whats the OA supposed to be?

x2suresh · Answer

No You can't assume/generalize

1) Xi = Xi-1/2 
 --> Xi-1/2 = Xi 
 --> X1= X2*2 
We don't the value of X2..
Insufficient
2) X5= X4/ (X4+1)
 insufficient.. we can't generalize this formula.

combine
X5= X4/ (X4+1) 
--> you can find the X
X5 = X4/2
Solve these two equations will get the value of X4
using X4 value and equation (1) you can find X3 
similarly using X3 value and equation (1) you can find X2
similarly using X2 value and equation (1) you can find X1

together sufficient.

durgesh79 · Answer

combining the two, we get x4.
once we have x4, we can find x3 using statement 1, remember statement 1 is for any i > 1, so it'll work for i = 4,3,2
at i = 2, we'll can find x1

if the term series is given is given and no condition is

Prep Toolkit

Top 5 GMAT Debrief Videos

615 to 715 in 15 Days (Ria's Strategies)

More than Quant/Verbal Abilities: Speed vs. Accuracy

745 with Only Self-Prep and GMAT Club

From 555 to 765: 210-point Improvement

Perfect 805 Score Debrief by Julia

My Rewards