1/2+5/6+11/12+19/20+…+379/380=_.
问题描述:
+1 2
+5 6
+11 12
+…+19 20
=______. 379 380
答
+1 2
+5 6
+11 12
+…+19 20
,379 380
=(1-
)+(1-1 2
)+(1-1 6
)+(1-1 12
)+…+(1-1 20
),1 380
=19-(
+1 2
+1 6
+1 12
+…+1 20
),1 380
=19-(1-
+1 2
-1 2
+1 3
-1 3
+…+1 4
-1 19
),1 20
=19-1+
,1 20
=18
.1 20
故答案为:18
.1 20