When adding a fraction and its reciprocal, ba+ab, you can use the formula:
ba+ab=2+ab(a−b)2
For example, 75+57=2+7⋅5(7−5)2=2+354=2354.
A popular variation involves a slight modification, like 1311+112. This can be rewritten as (1311+1113)−1111, allowing you to use the trick and then adjust the result.