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AS # 17

by oquiella » Sat Oct 24, 2015 12:32 pm
17. How many persons are there in the queue?
(1) In the queue, Adam is 15th from the front and Eve is 20th from the back
(2) In the queue, there are eight persons in between Adam and Eve.

aM I TO ASSUME ADAM IS AHEAD EVE?
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Source: — Data Sufficiency |
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by MartyMurray » Sat Oct 24, 2015 6:51 pm
NO. Definitely not.

That's the trick of this question.

If you were to assume that Adam is ahead of Eve, then the statements would be sufficient, but there is not really any reason to assume that, and the correct answer is that they are not sufficient.
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by Brent@GMATPrepNow » Fri Oct 30, 2015 7:57 am
oquiella wrote:How many persons are there in the queue?

(1) In the queue, Adam is 15th from the front and Eve is 20th from the back
(2) In the queue, there are eight persons in between Adam and Eve.
Target question: How many persons are there in the queue (line)?

Statement 1: In the queue, Adam is 15th from the front and Eve is 20th from the back
There are several scenarios that that satisfy statement 1. Here are two:
Case a: (FRONT)XXXXXXXXXXXXXXAXXXXXXXXEXXXXXXXXXXXXXXXXXXX(BACK). In this case there are 42 people in line
Case b: (FRONT)XXXXXEXXXXXXXXAXXXXXXXXXX(BACK). In this case there are 25 people in line
Since we cannot answer the target question with certainty, statement 1 is NOT SUFFICIENT

Statement 2: In the queue, there are eight persons in between Adam and Eve.
Tons of different scenarios possible.
Since we cannot answer the target question with certainty, statement 2 is NOT SUFFICIENT

Statements 1 and 2 combined
There are still two scenarios that that satisfy BOTH statements:
Case a: (FRONT)XXXXXXXXXXXXXXAXXXXXXXXEXXXXXXXXXXXXXXXXXXX(BACK). In this case there are 42 people in line
Case b: (FRONT)XXXXXEXXXXXXXXAXXXXXXXXXX(BACK). In this case there are 25 people in line
Since we cannot answer the target question with certainty, the combined statements are NOT SUFFICIENT

Answer = E

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by Max@Math Revolution » Sun Nov 01, 2015 9:01 am
Forget conventional ways of solving math questions. In DS, Variable approach is the easiest and quickest way to find the answer without actually solving the problem. Remember equal number of variables and independent equations ensures a solution.

17. How many persons are there in the queue?
(1) In the queue, Adam is 15th from the front and Eve is 20th from the back
(2) In the queue, there are eight persons in between Adam and Eve.

In the original condition, there is one variable (n), but we need to know numbers for both Adam and Eve, so there are 3 variables, and we therefore need 3 equations. There are only 2 equations given from the conditions, so there is high chance (E) will be the answer.

If we look at the conditions together,
If Adam is in front of Eve, the total number becomes 43, and 26 if Eve is in front of Adam. Therefore, the answer becomes (E).
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