Any fraction with a one as the numerator and a number equal to or greater than three as the denominator will be less than 1/2. As a general rule, if the denominator is more than twice as large as the numerator, the fraction will be smaller than 1/2. For example, 2/9 is less than 1/2.
In order to compare the size of fractions, they must have a common denominator. With a common denominator, the fraction with a smaller numerator is smaller. As an example, 1/2 and 2/9 could be re-written as 9/18 and 4/18 respectively. It is clear that 4/18, or 2/9 is the smaller of the pair.