IMO A is the answer.
from 1 ) put j = 2 we have
x2 = x1 / 2
or x1 = 2x2
as far as 2nd is concerned, it shows relation between and 4th and 5th term and in no way specifies the general term to calculate x1.
Please share the correct answer.
Arithmetic Sequence - NEED HELP.....
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Source: Beat The GMAT — Data Sufficiency |
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dhanda.arun
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amitansu
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It's a nice tricky prob.....
Even stem 2 confused me a little bit, here is how to solve...
From stem 1 : we can get x2=x2-1/2 (by taking j value more than 1)
=> x2=x1/2
and x3=x2/2; x4=x3/2 ; x5=x4/2 and so on...
But by knowing this we can't identify what is x1 or the first term.
x1 can be 32 then x2 would be 16 and x3 would be 8 and so on....
if x1 is 16 then x2 would be 8; x3 would be 4 and so on...
So insufficient.
From stem 2 we get x5=x4/x4+1 ,no help at all as we cant define the series.
Combining these two...
we know from (1) x5=x4/2 and from (2) x5=x4/x4+1
so x4+1=2 [comparing (1) and (2) ]
=> x4=2-1=1
then x3=2*x4=2
then x2=2*x3=2*2=4
so, x1=2*x2=2*4=8 (see that x5 would be x4/(x4+1)=1/1+1=1/2.
So ans is C.
Amit
Even stem 2 confused me a little bit, here is how to solve...
From stem 1 : we can get x2=x2-1/2 (by taking j value more than 1)
=> x2=x1/2
and x3=x2/2; x4=x3/2 ; x5=x4/2 and so on...
But by knowing this we can't identify what is x1 or the first term.
x1 can be 32 then x2 would be 16 and x3 would be 8 and so on....
if x1 is 16 then x2 would be 8; x3 would be 4 and so on...
So insufficient.
From stem 2 we get x5=x4/x4+1 ,no help at all as we cant define the series.
Combining these two...
we know from (1) x5=x4/2 and from (2) x5=x4/x4+1
so x4+1=2 [comparing (1) and (2) ]
=> x4=2-1=1
then x3=2*x4=2
then x2=2*x3=2*2=4
so, x1=2*x2=2*4=8 (see that x5 would be x4/(x4+1)=1/1+1=1/2.
So ans is C.
Amit
