| 脱式计算.(能简算的要简算) (1)0.125× +1.875÷4 | (2)27×99 |
| (3)30.1-16.8÷3.5×6.2 | (4) ×2.5× ×0.4 |
(5) ÷[ (- )÷ ] | (6)( - × )÷ . |
+1.875÷4,=0.125×
+1.875×
,=(0.125+1.875)×
,=2×
,=
;(2)27×99,
=27×(100-1),
=2700-27,
=2673;
(3)30.1-16.8÷3.5×6.2,
=30.1-4.8×6.2,
=30.1-29.76,
=0.34;
(4)
×2.5×
×0.4,=(
×
)×(2.5×0.4),=1×1,
=1;
(5)
÷[(
-
)÷
],=
÷[
÷
],=
÷
,=
×
,=
;(6)(
-
×
)÷
,=(
-
)÷
,=
÷
,=1.
分析:(1)把除法改为乘法,运用乘法分配律简算;
(2)把99看作100-1,运用乘法分配律简算;
(3)先算除法和乘法,再算减法;
(4)运用乘法交换律与结合律简算;
(5)先算小括号内的,再算中括号内的,最后算括号外的;
(6)先算括号内的乘法,再算括号内的减法,最后算括号外的除法.
点评:此题考查了四则混合运算,注意运算顺序和运算法则,灵活运用所学的运算律简便计算.