Subtracting unlike denominators

You change unlike denominators to like denominators by comparing the two denominators first:

You have 7/8 & 1/2...7/8 is fine, but 1/2 can be converted to something like #/8 [since 7/8 has 8 as its denominator] by multiplying both the numerator and denominator by 4 --> 1*4 / 2*4 = 4/8.

Now, we can easily subtract --> 7/8 - 4/8 = (7-4)/8 = 3/8.