While Preparing for Quantitative aptitude tests, questions on Number system HCF and LCM are asked frequently.
Here we have provided Shortcuts and tricks to calculate HCF and LCM in just 5 seconds!
How to claculate HCF and LCM
To calculate the highest common factor (HCF) of two or more numbers, you can use the following steps:

List the factors of each number. The factors of a number are the integers that divide evenly into that number. For example, the factors of 12 are 1, 2, 3, 4, 6, and 12.

Find the common factors of the numbers. These are the factors that appear in the lists for each number.

Choose the greatest common factor. This is the highest common factor (HCF) of the numbers.
For example, to find the HCF of 12 and 18:

List the factors of 12: 1, 2, 3, 4, 6, and 12 List the factors of 18: 1, 2, 3, 6, 9, and 18

Find the common factors of the numbers: 1, 2, 3, and 6

The greatest common factor is 6.
To calculate the least common multiple (LCM) of two or more numbers, you can use the following steps:

List the multiples of each number. The multiples of a number are the integers that the number can be multiplied by to produce a new integer. For example, the multiples of 3 are 3, 6, 9, 12, 15, etc.

Find the least common multiple. This is the smallest multiple that appears in the lists for each number.
For example, to find the LCM of 12 and 18:

List the multiples of 12: 12, 24, 36, 48, 60, etc. List the multiples of 18: 18, 36, 54, 72, 90, etc.

The least common multiple is 36.
Note that there are also formulas for calculating the HCF and LCM of two numbers. To find the HCF of two numbers, you can use the formula:
HCF = (a * b) / GCD(a, b)
where a and b are the two numbers, and GCD(a, b) is the greatest common divisor of a and b.
To find the LCM of two numbers, you can use the formula:
LCM = (a * b) / GCD(a, b)
where a and b are the two numbers, and GCD(a, b) is the greatest common divisor of a and b.