By bringing them both to the same/common denominator.
1/4 and 1/3
Which is larger? 12 is the common denominator here and to convert the fraction we multiply them by a form of 1.
3*1/3*4 = 3/12
4*1/4*3 = 4/12
By this method we see that 1/3 is larger than 1/4
