Binary to octal and hexadecimal:
To convert the number from binary to octal we make groups of 3 bits starting from the decimal point (in case of fractions) and from right most bit (in case of integers) and write the corresponding octal equivalent of those 3 bits every time.
The process of replacing the long strings of 1 & o with the shorter strings like Octal & hexadecimal equivalents is known as chunking.
Hexadecimal and octal to binary:
To do the above we convert the digits into their corresponding binary equivalents of 3-bits and 4-bits for octal and hexadecimal numbers respectively.