The CSAT (Civil Services Aptitude Test) requires strict logical clarity. Below is the ultimate compendium of CSAT topics explained in English, complete with solved examples and shortcuts. We have categorized this into three main modules: Quantitative Aptitude, Logical Reasoning, and Reading Comprehension.
Module 1: Quantitative Aptitude (Numeracy)
Topic A: Number System & Divisibility
The Number System is the absolute foundation of CSAT. You must master divisibility rules, remainders, and unit digits.
Concept: Divisibility by 8 and 9
A number is divisible by 8 if its last three digits are divisible by 8. A number is divisible by 9 if the sum of all its digits is a multiple of 9.
Example (UPSC pattern): If a 9-digit number 985x3678y is divisible by 72, find the value of (4x – 3y).
Solution: 72 = 8 x 9. So the number must be divisible by both 8 and 9.
Step 1 (Divisibility by 8): The last 3 digits ’78y’ must be divisible by 8. By trial, 784 is divisible by 8. So, y = 4.
Step 2 (Divisibility by 9): Sum of digits = 9+8+5+x+3+6+7+8+4 = 50 + x. The next multiple of 9 is 54. So, x = 4.
Answer: (4*4 – 3*4) = 16 – 12 = 4.
Topic B: Time, Speed, and Distance
Concept: Relative Speed
If two objects move in the same direction, relative speed = (S1 – S2). If they move in opposite directions, relative speed = (S1 + S2).
Example: A train 150m long is running at 60 km/hr. How long will it take to cross a person walking at 6 km/hr in the opposite direction?
Solution: Opposite direction = Add speeds. Relative speed = 60 + 6 = 66 km/hr.
Convert to m/s: 66 * (5/18) = 55/3 m/s.
Time = Distance / Speed = 150 / (55/3) = (150 * 3) / 55 = 8.18 seconds.
Module 2: Logical Reasoning
Topic A: Syllogisms
Concept: Always use Venn Diagrams. Never assume real-world facts. If the statement says “All cats are dogs”, treat it as mathematical truth.
Example:
Statement 1: All cups are books.
Statement 2: Some books are shirts.
Conclusion I: Some cups are shirts.
Conclusion II: Some shirts are books.
Solution: Draw a circle for Cups completely inside Books. Draw a circle for Shirts intersecting Books. Does the Shirts circle have to intersect Cups? No. So Conclusion I is invalid. However, since the Shirts circle intersects Books, Conclusion II is logically 100% valid. Answer: Only II follows.
Topic B: Direction Sense
Concept: Use Pythagoras theorem (A² + B² = C²) for shortest distance.
Example: A man walks 3 km North, turns right and walks 4 km. What is the shortest distance from the starting point?
Solution: He forms a right-angled triangle with sides 3 and 4. The hypotenuse = √(3² + 4²) = √(9+16) = √25 = 5 km.
Module 3: Reading Comprehension
The Golden Rule: The answer is ALWAYS inside the passage. Words like “Always, Never, All, None, Only” in the options are usually red flags for incorrect options (extreme statements).
Example Question Types:
– Crux/Central Idea: What is the main message the author is trying to convey?
– Inference: What logical conclusion can be drawn that isn’t explicitly stated but is heavily implied?