dễ nhưng ko tính

\(=\frac{111}{11}\)

111/11

tick chao minh nha

là 111/11

tik nha bạnNguyễn thị Hằng  yêu quý!

Tớ sửa chút, phải bằng 10

  1/2 + 5/6 + 11/12 + ... + 89/90 + 109/110 + 10/11

= (1 - 1/2) + (1 - 1/6) + (1 - 1/12) + ... + (1 - 1/90) + (1 - 1/110) + 10/11

= (1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1) - (1/1*2 + 1/2*3 + 1/3*4 + ... + 1/10*11) + 10/11

= 9 - (1 - 1/11) + 10/11

= 9 - 10/11 + 10/11 = 9

T=1/2+5/6+11/12+...+89/90+109/110+10/11

T= (1 -1/2) + ( 1 - 1/6) + (1-1/12) + (1-1/20)+(1-1/30)+... + (1 - 1/90) + (1- 1/110) + 10/11

T= 1x10 –(1/2+1/6+1/12+1/20+……..+1/90+1/110)+10/11

T=10 – (1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+……+1/9-1/10+1/10-1/11)+ 10/11

T= 10 – (1-1/11)+10/11 = 10-10/11+10/11

T=10

\(A=\left(1-\frac{1}{2}\right)+\left(1-\frac{1}{6}\right)+\left(1-\frac{1}{12}\right)+....+\left(1-\frac{1}{90}\right)+\left(1-\frac{1}{110}\right)+\frac{10}{11}\)

\(=10-\left(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+....+\frac{1}{10.11}\right)+\frac{10}{11}=10-\left(1-\frac{1}{11}\right)+\frac{10}{11}=10\)

110 -10 > X5 + 5X > 90

 100 > X0 + 5 + 50 + X > 90

100 > XX + 55 > 90

100 - 55 > XX + 55 - 55 > 90 - 55

45 > XX > 35

XX = 44 SUY RA X = 4

110 - 10 > X5 + 5X > 90

\(\frac{1}{10}+\frac{1}{20}+\frac{1}{30}+...+\frac{1}{90}+\frac{1}{110}\)

\(=\frac{1}{10}+\frac{1}{4.5}+\frac{1}{5.6}+...+\frac{1}{9.10}+\frac{1}{10.11}\)

\(=\frac{1}{10}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+...+\frac{1}{9}-\frac{1}{10}+\frac{1}{10}-\frac{1}{11}\)

\(=\frac{1}{10}+\frac{1}{4}-\frac{1}{11}\)

\(=\frac{57}{220}\)

   \(\frac{1}{10}+\frac{1}{20}+\frac{1}{30}+...+\frac{1}{90}+\frac{1}{110}\)

\(=\frac{1}{10}+\frac{1}{4.5}+\frac{1}{5.6}+...+\frac{1}{9.10}+\frac{1}{10.11}\)

\(=\frac{1}{10}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+...+\frac{1}{9}-\frac{1}{10}+\frac{1}{10}-\frac{1}{11}\)

\(=\frac{1}{10}+\frac{1}{4}-\frac{1}{11}\)

\(=\frac{22}{220}+\frac{55}{220}-\frac{20}{220}\)

\(=\frac{22+55-20}{220}\)

\(=\frac{57}{220}\)

t=(1-1/2+1-1/6+1-1/12+..........+1-1/90+1-1/110)-10/11

t=(1+1+1+...........+1+1)-(1/2+1/6+1/12+.......+1/90+1/110)-10/11

có 10 số 1 vì từ 1/2 đến 109/110 có 10 p/số

t=1.10-(1/1.2+1/2.3+1/3.4+.........+1/9.10+1/10.11)-10/11

t=10-(1-1/2+1/2_1/3+1/3_1/4+.............+1/9-1/10+1/10-1/11)-10/11

t=10-(1-1/11)-10/11

t=10-10/11-10/11

t=10-(10/11+10/11)

t=10-10/11.2

t=10-20/11

t=110/11-20/11

t=90/11

Đặt A=90+110+132+...+930

=9.10+10.11+11.12+...+30.31

=>3A=3.9.10+3.10.11+...+3.30.31

=9.10.11-8.9.10+10.11.12-9.10.11+....+30.31.32-29.30.31

=30.31.32-8.9.10

=29040

=>A=29040:3=9680