(1)1.25×3.9×2.4=1.25×0.8×(3×3.9)=1×11.7=11.7;(2)0.88×99+0.88=0.88×(99+1)=0.88×100=88;(2)0.98-0.036-0.264=0.98-(0.036+0.264)=0.98-0.3=0.68.