If there denominator is the same subtract the numerator and copy the denominator, example: 2/4 - 1/4 =1/4.
but if not, find first there least common factor.
example: 1/2-1/4 =
there common factor is 4
there new denominator will be 4. then you divide 4 into the denominator of the first fraction which is 2 and multiply the answer to the numerator 1 the answer will be 2. the answer 2 will become the new numerator of the first fraction. do the same on the second
1/2-1/4 = 2/4-1/4 = 1/4
if the denominator doesn't have the common factor.
multiply the two denominator 2 and 9 you will get 18. 18 will be the new denominator. divide 18 with the denominator of the first fraction which is 2 you will 9. 9 multiply to the numerator 1 is equal to 9. that would be the new numerator. do the same thing on the second fraction.
1/2-1/9 = 9/18 - 2/18 = 7/18