\(\frac{1}{2}+\frac{5}{6}+\frac{11}{12}+\frac{19}{20}+...+\frac{89}{90}\)

\(=1-\frac{1}{2}+1-\frac{1}{6}+1-\frac{1}{12}+1-\frac{1}{20}+...+1-\frac{1}{90}\)

\(=9-\left(\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+...+\frac{1}{90}\right)\)

\(=9-\left(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+...+\frac{1}{9.10}\right)\)

\(=9-\left(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+....+\frac{1}{9}-\frac{1}{10}\right)\)

\(=9-\left(1-\frac{1}{10}\right)\)

\(=9-\frac{9}{10}=\frac{81}{10}\)

a) \(2\frac{2}{5}\cdot\frac{25}{18}=\frac{12}{5}\cdot\frac{25}{18}=\frac{300}{90}=\frac{10}{3}\)

b) \(\frac{9}{11}:2\frac{5}{2}\cdot2\frac{3}{4}=\frac{9}{11}.\frac{2}{9}\cdot\frac{11}{4}=\frac{1}{2}\)

c) \(10:\frac{35}{24}:\frac{36}{7}=10\cdot\frac{24}{35}\cdot\frac{7}{36}=\frac{4}{3}\)

d) \(10,77\cdot9,8+5,23\cdot9,8=9,8\cdot\left(10,77+5,23\right)=9,8\cdot16=156,8\)

e) \(1,26\cdot3,6:0,28-6,2=16,2-6,2=10\)

là sao hả cậu?

\(2\frac{2}{5}\) x \(\frac{25}{18}\) = \(\frac{12}{5}x\frac{25}{18}=\frac{10}{3}\)                  x = nhân

\(\frac{9}{11}:2\frac{5}{2}x2\frac{3}{4}\) = \(\frac{9}{11}:\frac{9}{2}x\frac{11}{4}=\frac{2}{11}x\frac{11}{4}=\frac{1}{2}\)

\(10:\frac{35}{24}:\frac{36}{7}=\frac{48}{7}:\frac{36}{7}=\frac{4}{3}\)

\(10,77x9,8+5,23x9,8=\left(10,77+5,23\right)x9,8=156,8\)

\(1,26x3,6:0,28-6,2=4,536:0,28-6,2=16,2-6,2=10\)

bạn nói rõ hơn đi

a) \(=\frac{3}{17}-\frac{2}{345}+\frac{5}{12}+\frac{2}{345}-\frac{3}{17}+\frac{1}{12}\)

\(=\left(\frac{3}{17}-\frac{3}{17}\right)+\left(\frac{2}{345}-\frac{2}{345}\right)+\left(\frac{5}{12}+\frac{1}{12}\right)\)

\(=\frac{6}{12}=\frac{1}{2}\)

b) \(=-\frac{49}{25}-\frac{5}{36}+\frac{4}{123}+\frac{49}{25}-\frac{4}{123}-\frac{1}{36}\)

\(=\left(-\frac{49}{25}+\frac{49}{25}\right)+\left(\frac{4}{123}-\frac{4}{123}\right)-\left(\frac{5}{36}+\frac{1}{36}\right)\)

\(=-\frac{6}{36}=-\frac{1}{6}\)

Cảm ơn

\(\frac{22}{5}x\frac{25}{18}=\frac{550}{90}=\frac{55}{9}\)

\(\frac{9}{11}:2\frac{5}{2}x2\frac{3}{4}=\frac{9}{11}:\frac{9}{2}x\frac{11}{4}=\frac{9}{11}x\frac{2}{9}x\frac{11}{4}=\frac{1}{2}\)

\(10:\frac{35}{24}:\frac{36}{7}=10x\frac{24}{35}x\frac{7}{26}=\frac{10}{1}x\frac{24}{35}x\frac{7}{26}=\frac{24}{13}\)

   10,77 x 9,8 + 5,23 x 9,8 

= (10,77 + 5,23) x 9,8 = 16 x 9,8 = 156,8

1,26 x 3,6 : 0,28 - 6,2 = 4,536 : 0,28 - 6,2=

16,2 - 6,2 = 10

20/11 x 33/23 x 69/180 =

1/1 x 3/1 x 3/9 =

3/1 x 1/3 = 1

(Câu cuối trong fx không có phần gạch giữa {S} nên mình ghi tạm ngoài này nha bạn!)

11/12-5/12=6/12=1/2

25/24-16/24=9/24=3/8

27/36-15/36=12/36=2/3

k cho mik nhé

a) = 30

b) = 5

c) = 70

a)12+24+35-2-14-25=30

b)1-2+3-4+5-6+7-8+9=5

c)25-12-3+24+36=70

a) = 30

b) = 5

c) = 70