Ta có:C=1/11+12+1/13+...+1/50
=(1/11+1/12+...+1/20)+(1/21+1/22+...+1/30)+(1/31+1/32+...+1/40)+(1/41+1/42+...+1/50)
=(1/20+1/20+...+1/20)+(1/30+1/30+...+1/30)+(1/40+1/40+...+1/40)+(1/50+1/50+...+1/50)
=1/20×10+1/30×10+1/40×10+1/50×10
Nhân với10 vì mỗi tổng đều có10 số hạng
=1/2+1/3+1/4+1/5
=30/60+20/60+15/60+12/60
=77/60
Mik học trên lớp tương tự bài đấy
Hok tốt
1/11 + 1/12 + 1/13 + ... + 1/49 + 1/50 > 16/15
1/11 + 1/12 + 1/13 + ... + 1/49 + 1/50 > 8/3
Cho c=1/11+1/12+1/13+...+1/49+1/50.
Chứng minh 11/10<C<5/2
CM: 11/10 bé hơn 1/11+1/12+1/13+...+1/49+1/50 bé hơn 5/2
S=1/10+1/11+1/12+1/13+1/14+.....+1/49.so sánh S với 1/50
1. Thực hiện phép tính ( tính nhanh )
a, -6/35 : -54/49
b,-5/7.2/11+5/7.9/11+1 1/5
c,( 1/3 + 3/4 - 13/12 ) : ( 12/13 +123/234 +1234/2345 )
bài 1:
a) 10\17+5\-13-11\25+7\17-8\13
b) 0,3-93\7-70%0-4\7
c)1\8+1\24+1\48+...+1\2400
d) 3\41-12\17+33\49
-----------------------------
12\41-48\17+132\49
CTR:
a, 1/20+1/21+1/22+...+1/49<13/12
b, 1/11+1/12+1/13+...+1/40>13/12
Tính hợp lí ( Giúp mk với )
A = (-4/5 + 4/3) + (-5/4 + 14/5) - 7/3
B = 8/3 x 2/5 x 3/8 x 10 x 19/92
C = -5/7 x 2/11 + (-5)/7 x 9/14 + 1/57
D = 12/19 x 7/15 x (-13)/17 x 19/12 x 17/13
E = 1/1x2 + 1/2x3 + 1/3x4 + ....+ 1/49 x 50
a)11/53+(32/47+-10/53)+-64/94+1/53+1/3
b) (-1+45/115+47/51)+(-9/23+-1/3)
c) -13/49+12/48+1/12+3/18
d) 13/15+(-4/5+7/18)+-5/12+1/16
