Important Formulas: Number System

Number System is an important topic in Quantitative Aptitude section of various competitive exams. It includes topics like divisibility, HCF and LCM, fractions, surds and indices, decimal fractions, etc. Here are some important formulas related to Number System.

Divisibility Rules:

- A number is divisible by 2, if its unit digit is 0, 2, 4, 6 or 8.
- A number is divisible by 3, if the sum of its digits is divisible by 3.
- A number is divisible by 4, if the number formed by its last two digits is divisible by 4.
- A number is divisible by 5, if its unit digit is 0 or 5.
- A number is divisible by 6, if it is divisible by both 2 and 3.
- A number is divisible by 8, if the number formed by its last three digits is divisible by 8.
- A number is divisible by 9, if the sum of its digits is divisible by 9.
- A number is divisible by 10, if its unit digit is 0.

HCF and LCM:

- HCF (Highest Common Factor) of two or more numbers is the largest number that divides each of them exactly.
- LCM (Least Common Multiple) of two or more numbers is the smallest number that is a multiple of each of them.

Fractions:

- A fraction is a part of a whole.
- The numerator is the top number of a fraction and represents the part of the whole.
- The denominator is the bottom number of a fraction and represents the whole.

Surds and Indices:

- A surd is an irrational number.
- An index is the power to which a number is raised.

Decimal Fractions:

- A decimal fraction is a fraction whose denominator is a power of 10.
- The place value of a digit in a decimal fraction is the value of the digit multiplied by the appropriate power of 10.

Conclusion:

These are some important formulas related to Number System that are often asked in various competitive exams. It is important to practice these formulas regularly to master the topic.