Data Sufficiency

...

1) INSUFF: we do not know anything about the sequence

X2=X1/2 and so on .. Just gives us the formula of terms in the sequence

2) gives relationship of X4 and X5 : INSUFF

Combine

X5=(X4)/(X4+1)
and from 1 we get X5=X4/2

2 equations we can solve and hence on further calculation using 1 we can get X1

Hence C

IMO E
after combining we get

X5=(X4)/(X4+1)
and X5=X4/2
this X4=1 and X5=1/2 this contradictory to the condition that the given sequence contains positive numbers.

Answer is C only.

If you read the question properly, it says, sequence of positive numbers x1,x2,x3,.... and not positive integers.

sreak1089 wrote:Answer is C only.

If you read the question properly, it says, sequence of positive numbers x1,x2,x3,.... and not positive integers.

I think I am getting all confused here..
are fractions numbers??

Yes fractions are very much numbers and by all means.
But fractions are NOT integers or whole numbers or natural numbers.
Fractions come under the definition of rational numbers.

I have given definitions below:


1) Integers: ...-5,-4,-3,-2,-1,0,1,2,3,4,5....
2) Natural numbers: 1,2,3,4,5,..... (Set of Positive numbers only)
3) Whole numbers: 0,1,2,3,4,5,....(Zero + Set of Positive numbers)
4) Rational numbers: Any number that can be expressed in
the form of p/q (where q != 0) is called a rational number.

tohellandback wrote:IMO E
after combining we get

X5=(X4)/(X4+1)
and X5=X4/2
this X4=1 and X5=1/2 this contradictory to the condition that the given sequence contains positive numbers.

This is a common DS rule interpretation error, so it's important to understand the mistake you made.

In DS, the information in the statements will NEVER contradict the conditions in the stem. The conditions in the stem may limit which numbers you are allowed to pick, but there will always be at least one number that satisfies both the stem and the statements.

So, if you end up with a seeming contradiction (i.e. no possible number), it does not mean that the answer is E - it means that you have made a mistake somewhere along the way.

Answer "E" states that the statements are insufficient to answer the question, not that there is no possible answer. Since there's no answer choice that reflects "there is no possible value for x", that's not a possible result of the exercise.

i got to x5=x4/2 but i couldn't see how to get x1.... dat's why i ended up choosng E... how can we get to x1?

Stuart Kovinsky wrote:

tohellandback wrote:IMO E
after combining we get

X5=(X4)/(X4+1)
and X5=X4/2
this X4=1 and X5=1/2 this contradictory to the condition that the given sequence contains positive numbers.

This is a common DS rule interpretation error, so it's important to understand the mistake you made.

In DS, the information in the statements will NEVER contradict the conditions in the stem. The conditions in the stem may limit which numbers you are allowed to pick, but there will always be at least one number that satisfies both the stem and the statements.

So, if you end up with a seeming contradiction (i.e. no possible number), it does not mean that the answer is E - it means that you have made a mistake somewhere along the way.

Answer "E" states that the statements are insufficient to answer the question, not that there is no possible answer. Since there's no answer choice that reflects "there is no possible value for x", that's not a possible result of the exercise.

thanks Stuart, I understand now. I hope I will remember that during the test