Adding and Subtracting Fractions with the Butterfly Method. Butterfly Fractions To add or subtract fractions the butterfly way, 1. Write the fractions side-by-side as usual and draw two wings along the diagonals made by the numerator of one fraction and the denominator of the other fraction and draw an antenna on each wing. 2. 3. 4. 5. The butterflies above for 3/4 + 2/5 and 3/4 – 2/5 illustrate the procedure. Like this: Like Loading...