To convert the decimal number 0.65 to binary, octal, and hexadecimal, first express it as a fraction (0.65 = 65/100 = 13/20) and then perform long division in the desired base. The process for octal and hexadecimal is similar, using multiplication and division by 8 and 16, respectively. After converting to binary, group the bits into threes for octal and fours for hexadecimal for easier conversion. Online tools can assist in checking your answers, but understanding the manual conversion process is essential for accuracy. Mastering these techniques will enhance your number conversion skills across different bases.