计算:1/2+(1/3+2/3)+(3/4+2/4+1/4)+(4/5+3/5+2/5+1/5)+…+(19/20+18/20+…+1/20)=_.
问题描述:
计算:
+(1 2
+1 3
)+(2 3
+3 4
+2 4
)+(1 4
+4 5
+3 5
+2 5
)+…+(1 5
+19 20
+…+18 20
)=______. 1 20
答
+(1 2
+1 3
)+(2 3
+3 4
+2 4
)+(1 4
+4 5
+3 5
+2 5
)+…+(1 5
+19 20
+…+18 20
),1 20
=
+1+11 2
+2+…+91 2
,1 2
=
+1 2
+2 2
+…+3 2
,19 2
=(1+2+…+19)÷2,
=(1+19)×19÷2÷2,
=95.
故答案为:95.