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Question

Read the given statements and conclusions carefully. Assuming that the information given in the statements is ture, even if it appears to be at variance with commonly known facts, decide which of the given conclusions logically follow(s) from the statements.

Statements:

All aero-planes are cars.

All helicopters are cars.

All cars are scooters.

Conclusions:

1. All helicopters are scooters.

2. Some aero-planes are helicopters.

3. No aero-plane is helicopter.

This question was previously asked in
SSC Stenographer 2019 Previous Year Paper (24-Dec-2020) (Shift 2)
The correct answer is

Conclusion 1 and either conclusion 2 or 3 follow.

Understanding the Logical Statements and Conclusions

This question asks us to analyze a set of statements and determine which conclusions logically follow from them. In logical reasoning problems like this, we must assume the given statements are true, even if they contradict common knowledge. Our task is purely to follow the logic from the statements to the conclusions.

The Given Statements:

  • All aero-planes are cars.
  • All helicopters are cars.
  • All cars are scooters.

The Given Conclusions:

  • 1. All helicopters are scooters.
  • 2. Some aero-planes are helicopters.
  • 3. No aero-plane is helicopter.

Analyzing the Relationships from the Statements

Let's break down the relationships described by the statements. We can think of these relationships using categories or sets.

  • "All aero-planes are cars" means the set of aero-planes is completely inside the set of cars. We can represent this as Aero-planes ⊂ Cars.
  • "All helicopters are cars" means the set of helicopters is completely inside the set of cars. We can represent this as Helicopters ⊂ Cars.
  • "All cars are scooters" means the set of cars is completely inside the set of scooters. We can represent this as Cars ⊂ Scooters.

Combining these, we see that both the set of aero-planes and the set of helicopters are inside the set of cars, and the set of cars is inside the set of scooters.

This implies a hierarchy: Aero-planes are in Cars, Helicopters are in Cars, and Cars are in Scooters.

So, we have: Aero-planes ⊂ Cars ⊂ Scooters and Helicopters ⊂ Cars ⊂ Scooters.

Analyzing Each Conclusion Logically

Conclusion 1: All helicopters are scooters.

Let's check if this follows from the statements.

  • Statement 2 says: All helicopters are cars (Helicopters ⊂ Cars).
  • Statement 3 says: All cars are scooters (Cars ⊂ Scooters).

If every helicopter is a car, and every car is a scooter, then it logically follows that every helicopter must also be a scooter. This is a transitive property of the "all are" relationship. Helicopters are inside the set of Cars, and the set of Cars is inside the set of Scooters. Therefore, the set of Helicopters must be inside the set of Scooters (Helicopters ⊂ Scooters).

Conclusion 1 logically follows from the statements.

Conclusion 2: Some aero-planes are helicopters.

Let's check this conclusion.

  • Statement 1 says: All aero-planes are cars (Aero-planes ⊂ Cars).
  • Statement 2 says: All helicopters are cars (Helicopters ⊂ Cars).

Both aero-planes and helicopters are subsets of cars. The statements tell us they are both inside the 'Cars' category, but they don't give us any information about the relationship between aero-planes and helicopters themselves.

Based on the statements, it is possible that:

  • The set of aero-planes and the set of helicopters overlap within the set of cars (meaning some aero-planes are helicopters, and some helicopters are aero-planes).
  • The set of aero-planes and the set of helicopters are separate and do not overlap within the set of cars (meaning no aero-plane is a helicopter, and no helicopter is an aero-plane).

Since the statements do not provide enough information to definitively say whether there is an overlap, Conclusion 2 ("Some aero-planes are helicopters") does not necessarily follow. It is a possibility, but not a certainty based *only* on the given statements.

Conclusion 2 does not necessarily follow on its own.

Conclusion 3: No aero-plane is helicopter.

Let's check this conclusion using the same statements as for Conclusion 2:

  • Statement 1 says: All aero-planes are cars (Aero-planes ⊂ Cars).
  • Statement 2 says: All helicopters are cars (Helicopters ⊂ Cars).

As discussed for Conclusion 2, the statements only place both aero-planes and helicopters inside the set of cars. They do not specify if these two subsets overlap or are mutually exclusive.

Based on the statements, it is possible that:

  • The set of aero-planes and the set of helicopters are separate (meaning no aero-plane is a helicopter). This would make Conclusion 3 true.
  • The set of aero-planes and the set of helicopters overlap (meaning some aero-planes are helicopters). This would make Conclusion 3 false.

Since the statements do not provide enough information to definitively say that there is no overlap, Conclusion 3 ("No aero-plane is helicopter") does not necessarily follow. It is a possibility, but not a certainty based *only* on the given statements.

Conclusion 3 does not necessarily follow on its own.

Evaluating Conclusions 2 and 3 Together

Notice that Conclusions 2 ("Some aero-planes are helicopters") and 3 ("No aero-plane is helicopter") cover the two possible scenarios regarding the relationship between aero-planes and helicopters: either they have some overlap, or they have no overlap.

Since the statements place both aero-planes and helicopters within the category of cars but provide no further information about their relationship to each other, we cannot definitively prove either Conclusion 2 or Conclusion 3. However, in reality, for any two categories (aero-planes and helicopters), either some elements of one are in the other, or no elements of one are in the other (assuming non-empty sets, which is typically the case in these problems unless stated otherwise).

Therefore, based on the logical possibilities derived from the statements, while we cannot pick one specifically, we know that either Conclusion 2 must be true (some overlap) or Conclusion 3 must be true (no overlap). They form a complementary pair where one must be true, but not both.

So, either Conclusion 2 or Conclusion 3 follows, but we cannot determine which one.

Combining the Valid Conclusions

From our analysis:

  • Conclusion 1: "All helicopters are scooters" - This logically follows from the statements.
  • Conclusions 2 & 3: "Some aero-planes are helicopters" and "No aero-plane is helicopter" - Neither follows individually as a certainty, but one of them must be true. Therefore, either Conclusion 2 or Conclusion 3 follows.

Combining these findings, the conclusions that follow are Conclusion 1, and either Conclusion 2 or Conclusion 3.

Revision Table: Logical Reasoning Summary

Statements Logical Implications
All aero-planes are cars. Aero-planes ⊂ Cars
All helicopters are cars. Helicopters ⊂ Cars
All cars are scooters. Cars ⊂ Scooters
Conclusion Analysis Follows?
1. All helicopters are scooters. Helicopters ⊂ Cars ⊂ Scooters ∴ Helicopters ⊂ Scooters Yes
2. Some aero-planes are helicopters. Aero-planes ⊂ Cars, Helicopters ⊂ Cars. Relationship between Aero-planes and Helicopters is unknown. Does Not Necessarily Follow
3. No aero-plane is helicopter. Aero-planes ⊂ Cars, Helicopters ⊂ Cars. Relationship between Aero-planes and Helicopters is unknown. Does Not Necessarily Follow

Additional Information: Syllogism Basics

This type of question is a form of syllogism, a type of logical argument that applies deductive reasoning to arrive at a conclusion based on two or more propositions (statements) that are assumed to be true.

Key terms in syllogisms often involve quantifiers like "All," "Some," and "No," describing the relationship between categories.

  • All A are B: Every member of category A is also a member of category B (A is a subset of B).
  • Some A are B: At least one member of category A is also a member of category B (A and B have at least one member in common; their intersection is not empty).
  • No A is B: No member of category A is a member of category B (The categories A and B are mutually exclusive; their intersection is empty).

When analyzing these problems, visualize the categories and their overlaps or containments based *strictly* on the given statements. Avoid using real-world knowledge. The logic must flow purely from the premises provided. The possibility of different diagrams (e.g., overlapping vs. separate circles for aero-planes and helicopters within cars) helps evaluate conclusions that aren't universally true in all possible scenarios allowed by the statements. If a conclusion is true in *all* possible diagrams, it follows. If it's true in *some* but false in others, it does not necessarily follow. If it's true in *some* and its opposite is true in *others*, then one of the two (the conclusion or its opposite) must be true, leading to an "either/or" scenario for those specific conclusions.

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Important Questions from Syllogism

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