Logical Reasoning - Logical Deduction - Discussion

In each of the following questions, three statements are given followed by four conclusions numbered I, II, III and TV. You have to take the given statements to be true even if they seem to be at variance with commonly known facts and then decide which of the given conclusions logically follows from the given statements disregarding commonly known facts.

10. 

Statements: All pencils are birds. All birds are skies. All skies are hills.

Conclusions:

  1. All pencils are hills.
  2. All hills are birds
  3. All skies are pencils.
  4. All birds are hills.

[A]. Only I and II follow
[B]. Only I and III follow
[C]. Only III and IV follow
[D]. All follow
[E]. None of these

Answer: Option E

Explanation:

All pencils are birds. All birds are skies.

Since both the premises are universal and affirmative, the conclusion must be universal affirmative (A-type) and should not contain the middle term. So, it follows that 'All pencils are skies'.

All birds are skies. All skies are hills.

As discussed above, it follows that 'All birds are hills'. Thus, IV follows.

All pencils are skies. All skies are hills.

Clearly, it follows that 'All pencils are hills'. Thus, I follows.

Hence, I and IV follow.


Ktbffh said: (Jan 10, 2014)  
Can somebody explain in any other way ? not able to get it !

Sebas said: (Nov 6, 2014)  
I think they did not provide the correct answer: Only I and IV follow.

Jhoren said: (Sep 29, 2015)  
The logic only flows one direction through these sentences.

For example, it tells us that all pencils are birds, but it does not tell us that all birds are pencils. It tells us all birds are skies, but it does not tell us that all skies are birds. And. It tells us that all skies are hills, but it does not tell us that all the hills are skies.

Therefore you can say that any logic flowing the one direction is a correct answer while any logic flowing the other direction is not.

Naresh said: (Feb 17, 2016)  
The answer the conclusion follows the statement.

Chima said: (May 10, 2016)  
Considering the premises "All pencils are birds, all birds are skies''.

The conclusion will be All pencils are skies. But All skies are pencils (conclusion III) IS THE CONVERSE of the conclusion. If conclusion III is not included it makes the explanation delusional.

Dharani said: (Mar 21, 2017)  
According to the given question conclusion 1&4 are correct.

Upendra Majhi said: (Jan 10, 2018)  
By venn diagram, I and IV are valid. If all birds are hills vide skies, "all hills are birds" is not valid. "Only some Hills are birds" is valid. Similarly if " all pencils are skies" is valid vide birds, only "some skies are pencils" is valid. All skies are pencils is not valid.

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