Question

Cho E =1/31+1/32+1/33+...+1/60

So sánh E với 4/5

Bác nào làm được thì giúp em với mai thi rùi

Answer 1

(1/51 +1/52+  1/53 +1/54+ 1/55 +1/56+  1/57 +1/58 + 1/59 +1/60)(1/51 +1/52+  1/53 +1/54+ 1/55 +1/56+  1/57 +1/58 + 1/59 +1/60)(1/51 +1/52+  1/53 +1/54+ 1/55 +1/56+  1/57 +1/58 + 1/59 +1/60)(1/51 +1/52+  1/53 +1/54+ 1/55 +1/56+  1/57 +1/58 + 1/59 +1/60)(1/51 +1/52+  1/53 +1/54+ 1/55 +1/56+  1/57 +1/58 + 1/59 +1/60)(1/51 +1/52+  1/53 +1/54+ 1/55 +1/56+  1/57 +1/58 + 1/59 +1/60)(1/51 +1/52+  1/53 +1/54+ 1/55 +1/56+  1/57 +1/58 + 1/59 +1/60)(1/51 +1/52+  1/53 +1/54+ 1/55 +1/56+  1/57 +1/58 + 1/59 +1/60)(1/51 +1/52+  1/53 +1/54+ 1/55 +1/56+  1/57 +1/58 + 1/59 +1/60)(1/51 +1/52+  1/53 +1/54+ 1/55 +1/56+  1/57 +1/58 + 1/59 +1/60)(1/51 +1/52+  1/53 +1/54+ 1/55 +1/56+  1/57 +1/58 + 1/59 +1/60)

Answer 2

E = 1/31+1/32+...+1/60

E > 1/40+1/40+...+1/40+1/41+1/42+...+1/60

E > 20/40+1/41+1/42+...+1/60

E > 1/2+1/60+1/60+...+1/60

E > 1/2 + 1/3 = 5/6

Mà 5/6 > 4/5

=> E > 4/5