6.3*9.9
=6.3x(10-0.1)
=6.3x10-6.3x0.1
=63-0.63
=62.37
7.34*6.4-6.4*3.25*0.72
= 7.34*6.4-6.4*2.34
=6.4x(7.34-2.34)
=6.4x5
=32哪来的2.343.25*0.72=2.34