问题
解答题
下面各题怎样算简便怎样算. (1)3643-74+6357-76 (2)19.99÷2
(3)8500÷25 (4)
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答案
(1)3643-74+6357-76
=3643+6357-(74+76),
=10000-150,
=9850;
(2)19.99÷2
-0.4×9.991 2
=19.99×0.4-0.4×9.99
=(19.99-9.99)×0.4,
=10×0.4,
=4;
(3)8500÷25=340;
(4)
+1 2
+1 6
+1 12
+1 20
+1 30
+1 42
+1 56 1 72
=
+1 1×2
+…+1 2×3
,1 8×9
=1-
+1 2
-1 2
+…+1 3
-1 8
,1 9
=1-
,1 9
=
.8 9