CAT

No, CAT is not necessary to get admission in MBA colleges in India. But yes, if you aim for top management colleges in India CAT is best exam to write. It gives you advantage of applying to most top B schools in India. The selection of entrance exam to write completely depends upon your choice of college. The first thing you should ask to yourself which or what kind of colleges you want to take admission. If you want to take admission in tier 1 and tier 2 B-schools then you must write CAT. But if you want to take admission in tier 3 or so on or some regional/ local college then CAT is not very much required and you can go for MAT CMAT state entrance exams, etc.
Thanks.

Hi,
CAT analyses the skills of the aspirant in four sections: Quantitative Aptitude, Verbal Ability, Logical & Analytical Reasoning and Data Interpretation. It is also a test of time management.
1. Mathematics or Quantitative Section
Some of the core concepts in Maths and quant subjects are:
Geometry
HCF & LCM
Averages
Trigonometry
Algebra
Partnership (Accounts)
Mensuration
Profit & Loss
Time-Speed-Distance
Ratios and Proportion
In-equations Quadratic and linear equations
Surds and Indices
Number system
Geometric Progression
Inequalities
Work and time
Percentages
Logarithms
2. English or Verbal Section
Prominent topics in this section are:
Fill in the blanks
Verbal Reasoning
Sentence completion
Grammar
Syllogisms
Jumbled paragraphs
Para Completion and inference
Contextual usage
Foreign language words used in English
Reading Comprehension
Analogies
Sentence correction
Verbal Logic
Different usage of same word
Idioms
Parajumbles
Antonyms
One word substitution
3. Analytical Reasoning Section
Important topics under AR are:
Blood Relations
Series
Proposition
Direction Sense
Coding-Decoding
Assumptions
Puzzles
Clocks and Calenders
Statements
Data Arrangement
Family Tree
Binary Logic
Seating Arrangement
Venn Diagram
Sets
Data Structures
Syllogism
4. Data Interpretation Section
Problems related to organized and unorganized data are quite common in this section. Core topics are as follows:
Tables
Pie Charts
Caselets
Bars
Line Graphs
Data Sufficiency.

Good CAT scores vary depending on the competitiveness of the IIMs you wish to attend. However, based on what we know about business school admissions in India and percentile-to-mark conversion, we can infer what a good score might be.
(If you're uncertain about the tier of the IIM you wish to attend, you can find the brief summary of Indian business school tiers here). Top-Tier Schools: Above 200, with the sectional score between 80 and 85 (possibly lower in data interpretation and logical reasoning). Second-Tier Schools: Above 120, with sectional scores in the 40s and 50s (possibly lower in data interpretation and logical reasoning).
Third-Tier Schools: Above 100, with sectional scores in the 30s and 40s (possibly lower in Data Interpretation and Logical Reasoning). Even if you haven't achieved these marks on the CAT though, remember that different schools weight the importance of the CAT differently. Furthermore, other factors, including your employment history and school record, can be equally or more important.