用竖式计算。(①②小题要验算)①51×26 = ②904÷3=③6.2+3.9= ④ 836÷4=
(2.4×1.5-1.5)÷0.7
(3.2+3.2+3.2+3.2) ×2.5
+-
3600÷45×90
×(+0.8÷)