A reciprocal is also sometimes called a multiplicative inverse. The reciprocal is one of a pair of numbers that when multiplied together equals 1. Being able to reduce a number to a fraction makes it easier to find the reciprocal. Simply transposing the numerator and the denominator in a reciprocal fraction will allow you to find the reciprocal.
If you want to find the reciprocal of a whole number the best method would be to turn the number into a fraction in which the original number is the denominator and the numerator is 1. If you encounters a situation where you need to find the reciprocal of a decimal number you will then need to divide 1 by that number.