1、2.4/0.25=(2.4x4)/(0.25x4)=9.6/1=9.6
2、9999*7778+3333*6666=3333*(3*7778+6666)
=3333*30000=99990000
3、 5.6*69.32+138.64*0.05+693.2*0.43
=5.6*69.32+69.32*4.3+138.64*0.05
=5.6*69.32+69.32*4.3+69.32**0.1
=69.32*(5.6+4.3+0.1)
=69.32*10
=693.2
4、999*1999=(1000-1)*1999=1999000-1999=1997001