①2.5×(4+0.8)×1.25 = 2.5×4+0.8×1.25
②9.8×100.1=9.8×100+0.1
③125×21.7+125×78.3=125×(21.7+78.3)
④17.5÷1.2+17.5÷8.8=17.5÷(1.2+8.8)