①X:40=2.5:44x=40×2.54x=100x=100÷4x=25;②1 1 4 :X=0.4:80.4x=8×1 1 4 0.4x=8×1.25x=10÷0.4x=25;③ × 3.5 = 4 0.5 0.5x=3.5×40.5x=14x=14÷0.5x=28.