Ta có : 

\(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{2013.2014}\)

\(=\)\(\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{2013}-\frac{1}{2014}\)

\(=\)\(1-\frac{1}{2014}\)

\(=\)\(\frac{2014}{2014}-\frac{1}{2014}\)

\(=\)\(\frac{2013}{2014}\)

Vậy \(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{2013.2014}=\frac{2013}{2014}\)

Dấu \(.\) là dấu nhân nhé 

Chúc bạn học tốt ~

\(\frac{1}{1\times2}+\frac{1}{2\times3}+\frac{1}{3\times4}+...+\frac{1}{2013\times2014}\)

\(=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{2013}-\frac{1}{2014}\)

\(=1-\frac{1}{2014}\)

\(=\frac{2013}{2014}\)

CHÚC BN HỌC TỐT!!!!!
 

\(\frac{15}{22}:\frac{33}{6}=\frac{4}{33}\)

\(\frac{15}{22}+\frac{y}{6}=\frac{4}{33}\)

\(\frac{y}{6}=\frac{15}{22}\div\frac{4}{33}\)

\(\frac{y}{6}=1\)

Vậy y = 6 

k mk nha 

\(\frac{1}{20}+\frac{1}{30}+\frac{1}{42}\)

\(=\frac{1}{4\cdot5}+\frac{1}{5\cdot6}+\frac{1}{6\cdot7}\)

\(=\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}\)

\(=\frac{1}{4}-\frac{1}{7}\)

\(=\frac{7}{28}-\frac{4}{28}\)

\(=\frac{3}{28}\)

    Chúc bạn học tốt

Ta có : 

\(\frac{1}{20}+\frac{1}{30}+\frac{1}{42}\)

\(=\)\(\frac{1}{4.5}+\frac{1}{5.6}+\frac{1}{6.7}\)

\(=\)\(\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}\)

\(=\)\(\frac{1}{4}-\frac{1}{7}\)

\(=\)\(\frac{3}{28}\)

Chúc bạn học tốt ~ 

\(\frac{3}{4}\times\frac{9}{7}\times\frac{11}{25}\)

\(=\frac{297}{700}\)

Chúc bn học tốt!!!!!

\(\frac{3}{4}x\frac{9}{7}x\frac{11}{25}\)

= \(\frac{3}{4}x\frac{11}{25}x\frac{9}{7}\)

=\(\frac{33}{100}x\frac{9}{7}\)

=\(\frac{297}{700}\)

là 6/25

= 6/25

1 phần 4 = 10 phần 40

2 phần 5= 16 phần 40

3 phần 2= 50 phần 40

=1009

1010 mà

Tính:

23×15 + 26×23 + 23×18 + 24×23 + 18×23 - 23

Nhóm lại:

= 23×(15 + 18 + 18 + 26 + 24) - 23
= 23×101 - 23
= 2323 - 23
= 2300

Kết quả: 2300 🤡

🤡🤡🤡Xin tick ạ !

\(23×15+26×23+23×18+24×23+18×23−23\)

\(=23×(15+26+18+24+18−1)\)

\(=23\times100\)

\(=2300\)

\(\frac{2}{5}+\frac{3}{5}=\frac{5}{5}=1\)

=1nha bạn