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no see the obvious

by lukaswelker » Thu Apr 17, 2014 9:17 am
Hey guys

I'm sure that for the following question, I'm probably blind to the obvious.

If sequence S has 240 terms, what is the 239th terms of S?

(1) Each term of S after the first term is 4 less than the preceding term.
(2) the 239th term of S is 952 less than the first term.

Can anybody help me see the pink elephant in the room?

Many thanks
Lukas
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Source: — Data Sufficiency |
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by ajaysingh24 » Thu Apr 17, 2014 11:39 am
lukaswelker wrote:Hey guys

I'm sure that for the following question, I'm probably blind to the obvious.

If sequence S has 240 terms, what is the 239th terms of S?

(1) Each term of S after the first term is 4 less than the preceding term.
(2) the 239th term of S is 952 less than the first term.

Can anybody help me see the pink elephant in the room?

Many thanks
Lukas
Each statement is only giving info about the common difference ...
I do not see any way in which it provide info about the first term ... according to me answer should be (E) ..
What is the official answer
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by amitmj » Fri Apr 18, 2014 2:00 am
The answer should be as follows:

For statement 1: As we don't know the starting number of the series, hence we will not be able to find
the 239th sequence in the list even though we know the common difference is 4

For statement 2: Since 239th term is 952 less than the first term, you can't find the first term as you don't know the common difference between any two terms. Also we are not given in this sentence that there is a common difference between any 2 consecutive number in the list.

Combining the first and second sentence, we see that common difference is 4 and 239th term minus 1st term is equal to 952. Using this we still have multiple values for 1st term (960, 956,952) etc. and corresponding 239th term (8, 4, 0) etc. Hence we dont have a single value for 239th term and hence the answer is E
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by sanju09 » Sun Apr 20, 2014 3:19 am
lukaswelker wrote:Hey guys

I'm sure that for the following question, I'm probably blind to the obvious.

If sequence S has 240 terms, what is the 239th terms of S?

(1) Each term of S after the first term is 4 less than the preceding term.
(2) the 239th term of S is 952 less than the first term.

Can anybody help me see the pink elephant in the room?

Many thanks
Lukas
Hi Lukas,

The pink elephant is in your pocket, strange why you cannot feel it.

(1) It suggests that the sequence consists of evenly spaced terms with the regular distinction of -4, but we know no term of the sequence to map it right. Insufficient

(2) 239th term - 1st term = -952, but we don't know the rule how it progresses, insufficient.

Combining, all we know is what we already knew, [spoiler]no fresh gossip.


Hence E[/spoiler]
The mind is everything. What you think you become. -Lord Buddha



Sanjeev K Saxena
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The Princeton Review - Manya Abroad
Lucknow-226001

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by Brent@GMATPrepNow » Sun Apr 20, 2014 8:03 am
lukaswelker wrote: If sequence S has 240 terms, what is the 239th terms of S?

(1) Each term of S after the first term is 4 less than the preceding term.
(2) the 239th term of S is 952 less than the first term.
IMPORTANT: Statement 2 can be directly inferred from statement 1.
That is, if each term is 4 less than the previous term (e.g., 19, 15, 11, etc) then we can conclude that term2 will be 4 less than term1.
We can also conclude that term3 will be 8 less than term1, and:
term4 will be 12 less than term1.
term5 will be 16 less than term1.
.
.
.
term239 will be 952 less than term1 (same as statement 2).

So, as you can see, statement 2 DOES NOT PROVIDE ANY EXTRA INFORMATION beyond the information that statement 1 provided.

So, if statement 1 is NOT SUFFICIENT (which is clearly the case), then statement 2 cannot be NOT SUFFICIENT.
More importantly, the statements combined are NOT SUFFICIENT.

Answer: E

I cover this concept in the following free video on data sufficiency strategies: https://www.gmatprepnow.com/module/gmat- ... cy?id=1109

Cheers,
Brent
Brent Hanneson - Creator of GMATPrepNow.com
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