Add 1 1/3 + (-5/6) = ?

1 1/3 = 4/3 (because (3 * 1 + 1) / 3)

We need both parts of sum to have common denominator.

Second part have denominator = 6.

When we multiply nominator and denominator of first part by 2 we get 8/6 (what is legit operation on fractions)

Now easily add:

8/6 + ( - 5/6) = 8/6 - 5/6 = 3/6 (here we can divide both nominator and denominator by 3 to get "nicer" result) = 1/2