1 / 2 + 1 / 5 = () 12 × 2 / 3 = () 9 / 10 × 5 / 18 = () 3 / 4 - 3 / 5 = () 3 / 7 × 21 = () 12 / 5 × 5 / 4 = () 2 / 13 × 39

1 / 2 + 1 / 5 = () 12 × 2 / 3 = () 9 / 10 × 5 / 18 = () 3 / 4 - 3 / 5 = () 3 / 7 × 21 = () 12 / 5 × 5 / 4 = () 2 / 13 × 39

1 / 2 + 1 / 5 = (7 / 10) 12 × 2 / 3 = (8) 9 / 10 × 5 / 18 = (1 / 4) 3 / 4 - 3 / 5 = (3 / 20) 3 / 7 × 21 = (9) 12 / 5 × 5 / 4 = (3) 2 / 13 × 39 = (6)