Alex, Billy, Charlie and Derrick are the leading environmentalists in

Question

12 Days of Christmas 🎅 GMAT Competition with Lots of Questions & Fun

Alex, Billy, Charlie and Derrick are the leading environmentalists in Pinaka, a country with only 20% of the land under forest. All four are often seen together in various seminars delivering lectures on environmental issues. In one such seminar on environmental sustainability, the first four slots for speakers were reserved for them. Due to prior commitments, Derrick showed his inability to speak in any of the first three slots and picked up the fourth slot.

When the organizers enquired about the sequence for remaining three, the following three statements were made by the environmentalists with the caveat that only one of them is speaking the truth.

Alex: “Billy is the first speaker”.
Billy: “Charlie is not the first speaker”.
Charlie: “Alex is not the third speaker”.

Select for  First Speaker  the environmentalist who has to deliver the first lecture, and for  Third Speaker  the environmentalist who has to deliver the third lecture. Make only two selections, one in each column.

Bunuel · Accepted Answer

Official Solution: We are given three statements, and only one of them is true. 1. Alex: “Billy is the first speaker.” 2. Billy: “Charlie is not the first speaker.” 3. Charlie: “Alex is not the third speaker.” We also know that Derrick is the fourth speaker . Step 1: Assume Alex's statement is true If Alex is telling the truth, then Billy must be the first speaker . Since only one statement can be true, Billy’s and Charlie’s statements must both be false. If Billy’s statement “Charlie is not the first speaker” is false, then Charlie must be the first speaker . However, this directly contradicts our assumption that Billy is the first speaker. This contradiction proves that Alex’s statement must be false . Step 2: Assume Billy's statement is true If Billy is telling the truth, then Charlie is not the first speaker . Since only one statement can be true, Alex’s and Charlie’s statements must both be false. Alex’s statement “Billy is the first speaker” is false, meaning Billy is not the first speaker. If neither Charlie nor Billy is the first speaker, then Alex must be the first speaker. However, if Alex is the first speaker, then Charlie’s statement “Alex is not the third speaker” would also be true, contradicting the rule that only one statement can be correct. This contradiction proves that Billy's statement must be false . Step 3: Analyze Charlie’s statement If Charlie is telling the truth, then Alex cannot be the third speaker . Since only one statement can be true, Alex’s and Billy’s statements must both be false. Alex’s statement “Billy is the first speaker” is false, meaning Billy is not the first speaker. Billy's statement “Charlie is not the first speaker” is false, meaning Charlie must be the first speaker . With Charlie as the first speaker and Alex not in the third slot, he must take the second slot, leaving Billy as the third speaker. This results in the order: Charlie - Alex - Billy . Correct answer: First Speaker "Charlie" Third Speaker "Billy" GMAT-Club-Forum-ghzeqlbn.png

VibhuAnurag · Answer

The first speaker is Charlie and the third speaker is Billy.

If Alex is speaking the truth --> Billy is #1. However, since Billy is lying, Charlie must be #1 --> Contradictory. Hence, Alex is lying.

If Billy is speaking the truth --> based on Alex and Billy's statements, Alex must be the first speaker. But, Charlie says that Alex is not the third speaker, and Charlie is lying, so Alex must be the third speaker as well --> Contradictory. Hence, Billy is lying and it is Charlie who is telling the truth.

--> The correct order is C, A, B, D.

unnati157 · Answer

Based on the text, we know that Derrick is the 4th speaker: _ _ _ D
The remaining statements are: 
Alex: “Billy is the first speaker”.
Billy: “Charlie is not the first speaker”.
Charlie: “Alex is not the third speaker”.

Assuming statement 1 is true and 2&3 are false:  
Billy is the first speaker: B _ _ D
'Charlie is not the first speaker' is also a true statement then since Billy is the first speaker
Since only one of them is telling the truth, this would not be the correct order

Assuming statement 2 is true and 1&3 are false:  
Charlie is not the first speaker: _ (maybe C) (maybe C) D
Billy is the first speaker is false: _ (maybe C or B) (maybe C or B) D
Alex is not the third speaker is false: _ (maybe C or B) A D
Since neither B or C would take up the first spot, this would not be the correct order

Assuming statement 3 is true and 1&2 are false:  
Alex is not the third speaker: (Maybe A) (Maybe A) _ D
Billy is the first speaker is false: (Maybe A) (Maybe A or B) (Maybe B) D
Charlie is not the first speaker is false: C A B D
This would be the only possible order making one statement true and the other statements false

Therefore final order: Charlie, Alex, Billy, Derrick

chetan2u · Answer

So, first three spots are taken by Alex, Billy and Charlie.

Let’s take each statement one by one.

1. Alex: “Billy is the first speaker”.
Let this statement be true.   So, Billy is the first speaker and the remaining two statements are false.  
But then Charlie is not the first speaker and the statement by Billy too becomes true. 
 We can say for sure that Billy is not the first speaker.

2. Billy: “Charlie is not the first speaker”.
Let this statement be true.   So, Charlie is not the first speaker and the remaining two statements are false.  
Thus, Billy is also not the first speaker from (1) above.  Means Alex is the first speaker 
However , this makes the statement 3 also true. 
 We can say for sure that Charlie is the first speaker.

Charlie: “Alex is not the third speaker”.
This statement HAS to be true. But let us see if other statements are true. 
We know from (2) that Charlie is the first speaker.
If Alex is not the third speaker, then he is the second speaker.

The sequence becomes Charlie, Alex and Billy. 
Solution: Charlie and Billy

Kinshook · Answer

Alex, Billy, Charlie and Derrick are the leading environmentalists in Pinaka, a country with only 20% of the land under forest. All four are often seen together in various seminars delivering lectures on environmental issues. In one such seminar on environmental sustainability, the first four slots for speakers were reserved for them. Due to prior commitments, Derrick showed his inability to speak in any of the first three slots and picked up the fourth slot.

When the organizers enquired about the sequence for remaining three, the following three statements were made by the environmentalists with the caveat that only one of them is speaking the truth.

Alex: “Billy is the first speaker”.
Billy: “Charlie is not the first speaker”.
Charlie: “Alex is not the third speaker”.

Select for  First Speaker  the environmentalist who has to deliver the first lecture, and for  Third Speaker  the environmentalist who has to deliver the third lecture. Make only two selections, one in each column.

Derrick is the Fourth Speaker.

Let no assume that first statement is true and other 2 are false
Billy is the first speaker. True
Charle is not the first speaker. 
Has to be true since Billy is the first speaker and Charlie is not. But only 1 statement is true
NOT POSSIBLE

Let no assume that second statement is true and other 2 are false
Billy is the first speaker. False
Billy is NOT the first speaker
Charlie is not the first speaker. True
Alex is the first speaker.
Alex is not the third speaker. 
Has to be true since Alex is the first speaker.
But only 1 statement is true
NOT POSSIBLE

Let no assume that third statement is true and other 2 are false
Billy is the first speaker. False
Billy is NOT the first speaker
Charlie is not the first speaker. False
Charle is the first speaker
Alex is not the third speaker. True
Alex is the second speaker
Billy is the third speaker.

vishal_gupta · Answer

1. If A is speaking truth, then other two will be speaking false. So, according to A, B is at 1st position. If we falsified the B's statement i.e. C is not at 1st, it implies C is at 1st. So, A's and B's statements contradict, hence A is speaking false.

2. f B is speaking truth, then other two will be speaking false. So, according to B, C is not at 1st position. So, C must be at 2nd or 3rd position. Falsifying C's statement 3rd position belong to A. But the only position left for B will be 1st, which is not possible as A's statement must be false. Hence B is also speaking false.

3. C must speak truth. So, A's position would be 1st or 2nd. Falsifying B's statement C will be at 1st position. Hence B will be at 3rd position. All conditions are satisfied.

So, correct ans is 1st position=C and 3rd position=B

Laila12618 · Answer

Charlie is telling the truth. 
Alex and Billy and lying.

Hence, Alex is not the third to speak by Charlie.
Billy is NOT the first to speak by Alex.
Charlie IS the first one to speak by Billy.

Three correct order is: Charlie -> Alex -> Billy

Posted from my mobile device

nnavin · Answer

Only one of them is speaking the truth.

Alex: “Billy is the first speaker”.
Billy: “Charlie is not the first speaker”.
Charlie: “Alex is not the third speaker”.

Let's go in the order of one person speaking the truth and how the rest of the statements change accordingly.

Scenario 1: Alex is speaking the truth. 
Statements:
Alex: “Billy is the first speaker”. -> True, hence Billy is the first speaker.
Billy: “Charlie is not the first speaker”. -> False, hence Charlie is the first speaker.
Charlie: “Alex is not the third speaker”. -> False, hence Alex is the third speaker.

A clear conflict between Alex's and Billy's statements hence not the correct scenario.

Scenario 2: Billy is speaking the truth. 
Statements:
Alex: “Billy is the first speaker”. -> False, hence Billy is not the first speaker.
Billy: “Charlie is not the first speaker”. -> True, hence Charlie is not the first speaker.
Charlie: “Alex is not the third speaker”. -> False, hence Alex is the third speaker.

From Alex's and Billy's statements, Alex has to be the first speaker since Billy and Charlie cannot be the first speaker. 
But Charlie's statement gives the conflict of Alex being the third speaker hence not the correct scenario.

Scenario 3: Billy is speaking the truth. 
Statements:
Alex: “Billy is the first speaker”. -> False, hence Billy is not the first speaker.
Billy: “Charlie is not the first speaker”. -> False, hence Charlie is the first speaker.
Charlie: “Alex is not the third speaker”. -> True, hence Alex is not the third speaker.

From Billy's statement, Charlie is the first speaker. From Charlie's statement, since Alex is not the third speaker he has to be the 2nd speaker and Billy is the 3rd speaker.
This scenario doesn't give rise to any conflict hence Charlie is speaking the truth and the order of speakers is Charlie, Alex, Billy.

missionmba2025 · Answer

The correct order is Charlie, Alex and Billy

1) If Alex is speaking the truth

We have a conflict on the first position. Alex claims Billy is the first speaker while as per Billy's statement , which is false, Charlie is the first speaker.

2) If Billy is speaking the truth

Alex: As per his statement Billy is either in the second and third place.
Billy: Charlie is not first
Charlie: Alex is third.

So who is at the first position ? No one ! Hence this is not correct.

3) If Charlie is speaking the truth

Alex: As per his statement Billy is either in the second and third place.
Billy: Charlie is first
Charlie: Alex is not third. First is taken, so Alex is second.

Hence the correct order is Charlie, Alex and Billy.

paulkim46 · Answer

Answer: First = Charlie; Third = Billy

Based on the information provided, we can deduce the following:

If Alex is telling the truth:
1 2 3 4
B D

If Billy is telling the truth: 
1 2 3 4
 C? C? D

If Charlie is telling the truth:
1 2 3 4
A? A? D

With that,

Alex  cannot  be telling the truth because if Alex  is  telling the truth, that means Charlie is speaking 2nd or 3rd, which means Billy is  also  telling the truth, and we know that only  1  of the speakers are telling the truth. So, we know  Billy is not the first speaker .

Billy also  cannot  be the truthteller, because - (if Billy is truthful) if Charlie is the 2nd speaker, Billy must be the 3rd speaker (since Billy can't be the 1st). However, this forces Alex to be the 1st speaker (see below), which cannot be true, since this would make Charlie  also truthful .
1 2 3 4
A C B D

Likewise, if (based on Billy's truthfulness) Charlie is the 3rd speaker, Billy must be the 2nd speaker, but again, this makes Charlie also truthful again - cannot be correct.
1 2 3 4
A B C D

Last, we have Charlie as the truth sayer, meaning Alex must be the first or second speaker. Alex cannot be the first speaker, since that would make Billy also truthful ("Charlie not first speaker"). Thus, Alex must be the 2nd speaker, leaving Charlie to be the 1st speaker and Billy the 3rd (see below).
1 2 3 4
C A B D

In this case, Charlie is telling the truth ("Alex is not the 3rd speaker"), Alex is lying ("Billy is the 1st speaker" = false), and Billy is also lying ("Charlie is not the 1st speaker" = false), satisfying all criteria.

Alex, Billy, Charlie and Derrick are the leading environmentalists in

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First Speaker	Third Speaker
		Alex
		Billy
		Charlie
		Derrick
		Cannot be determined

GMAT Two-part Analysis (TPA) Questions

Alex, Billy, Charlie and Derrick are the leading environmentalists in

Prep Toolkit

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My Rewards