Bài 1: Tính nhanh: a, 21.35-325.7 b,77-11.(30+7) c,85.(35-27)-35.(85-27) d,47.(45-15)-47.(45+15)

a, 21.35-325.7

=7.3.35-325.7

=7.(105-325)

=7.(-220)

=-1540

b,77-11.(30+7)

=11.7-11.(30+7)

=11.(7-30-7)

=11.(-30)

=-330

c, 85.(35-27)-35.(85-27)

=85.35-85.27-35.85+35.27

=(85.35-85.27-35.85)+35.27

=85.(35-27-35)+35.27

=-85.27+35.27

=27.(35-85)

=27.(-50)

=-1350

d, 47.(45-15)-47.(45+15)

=47.(45-15-45-15)

=47.(-30)

=-1410.