每千克螃蟹34元，买2千克的螃蟹，50元钱够用吗？
口算
78﹣0.8= 18×40= 910÷70= 1÷
=
﹣
=
3﹣
= 3.48+6.52=
×
=
÷
= 0.8﹣
=
直接写得数．
2/5﹣1/10= 16÷2/7= 1/2÷3/5= 1/7×1/7= 1/4×2/5=
5/6﹣1/2= 2/7×0+9= 3/5×1/21= 2/7×21= 14/17÷7=
1÷5﹣1/5= 4/7+4/7×6=（1/8+4/8）×4/5= 6×5÷1/2= 1/9÷1/3=
5/9×1/5÷5/9×1/5=
直接写出得数．
=
=
=
=
=
=
=
=
=
=
=
=
=
= 1﹣1%=
直接写出得数．
×12=
÷
=
×=
÷=
÷1=
﹣
=
+
= 20÷
=
×21=
÷
= 2÷10%= 16×25%=
直接写得数：
2.7﹣
= 5.6÷0.08=
÷
= 36×10%=
=
×9×
=
﹣0÷
+1= 1÷
﹣÷1=
小时：120分= 7﹣7÷8=