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JEE Main 2020 - 2 Sep (Morning)
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Animated Solution for Mathematics - Basic Mathematics: The contrapositive of the statement "If I reach the station in time, then I will catch the train" is:

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Visualized Solution

Understanding the Conditional Statement

  • Given statement: "If I reach the station in time, then I will catch the train."
  • This is a conditional statement of the form If , then .

Defining Proposition

  • Let be the first proposition (the condition).
  • : "I reach the station in time."

Defining Proposition

  • Let be the second proposition (the result).
  • : "I will catch the train."

Symbolic Representation

  • The original statement can be written symbolically as:
  • Read as " implies "

The Concept of Contrapositive

  • The contrapositive of a conditional statement is defined as:
  • Where denotes the negation (NOT) of the proposition.

Negating Proposition

  • Negate the second proposition and move it to the front:
  • : "I will not catch the train."

Negating Proposition

  • Negate the first proposition and move it to the back:
  • : "I do not reach the station in time."

Constructing the Final Statement

  • Combine and into the form If , then :
  • "If I will not catch the train, then I do not reach the station in time."

Matching with Options

  • Compare the result with the given options:
  • Option 1: (Converse)
  • Option 2: (Incorrect)
  • Option 3: (Inverse)
  • Option 4: (Contrapositive)
  • The correct option is 4.

The Sigma Insight: Theory of Indices

Solution Diagram

The Anatomy of a Statement

We are given the statement: "If I reach the station in time, then I will catch the train." In the language of logic, this is a conditional statement.
We can represent it symbolically as . Here, is the condition: "I reach the station in time", and is the result: "I will catch the train".
The arrow represents the logical implication. It tells us that if happens, is guaranteed to follow. It is a simple, beautiful flow of causality.

The Contrapositive Dance

The question asks for the contrapositive. This is where many students stumble, but you won't!
The contrapositive of is defined as . The symbol denotes negation, or "NOT".
So, we are saying: "If NOT , then NOT ". To find the contrapositive, we perform two steps: 1. Negate both propositions. 2. Swap their positions.
Let us apply this to our statement. Our is "I will catch the train". Its negation, , is "I will not catch the train".
Our is "I reach the station in time". Its negation, , is "I do not reach the station in time".
Now, we put them together in the form : "If I will not catch the train, then I do not reach the station in time."

Why It Matters

You might wonder, why do we do this? Why not just swap them?
If we just swapped them, we would get the converse, which is not logically equivalent. The beauty of the contrapositive is that it is logically equivalent to the original statement.
If the original statement is true, the contrapositive must also be true. It is a mirror image that preserves the truth value.

The JEE Mindset

In the exam, you will encounter many such logical statements. The key is to stay calm, define your and clearly, and apply the transformation rule systematically.
Do not let the English language confuse you; translate it into the symbolic language of logic, and the answer will reveal itself.
You have the tools, you have the logic, and now you have the understanding. Go forth and conquer these problems with confidence!

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