2.5×(5.5×5-0.55×10)=2.5×(5.5×5-5.5×1)=2.5x(5.5x6)=2.5x33=2.5x30 +2.5x3=75+7.5=82.5
=2.5×（0.55×50-0.55×10）=2.5×0.55×（50-10）=2.5×40×0.55=55
