16

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

\(\dfrac{2}{3}+\dfrac{5}{3}=\dfrac{2+5}{3}=\dfrac{7}{3}\)

\(\dfrac{3}{8}+\dfrac{4}{8}=\dfrac{3+4}{8}=\dfrac{7}{8}\)

\(\dfrac{6}{9}+\dfrac{2}{9}=\dfrac{6+2}{9}=\dfrac{8}{9}\)

\(\dfrac{12}{18}+\dfrac{7}{18}=\dfrac{12+7}{18}=\dfrac{19}{18}\)

\(\dfrac{7}{4}+\dfrac{2}{4}=\dfrac{7+2}{4}=\dfrac{9}{4}\)

\(B=\dfrac{5}{3}x\left(\dfrac{1}{2}+\dfrac{1}{6}+\dfrac{1}{12}+\dfrac{1}{20}+...+\dfrac{1}{90}\right)=\)

\(=\dfrac{5}{3}x\left(\dfrac{1}{1x2}+\dfrac{1}{2x3}+\dfrac{1}{3x4}+\dfrac{1}{4x5}+...+\dfrac{1}{9x10}\right)\)

\(C=\dfrac{2-1}{1x2}+\dfrac{3-2}{2x3}+\dfrac{4-3}{3x4}+...+\dfrac{10-9}{9x10}=\)

\(=1-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{4}+...+\dfrac{1}{9}-\dfrac{1}{10}=\)

\(=1-\dfrac{1}{10}=\dfrac{9}{10}\)

\(\Rightarrow B=\dfrac{5}{3}xC=\dfrac{5}{3}x\dfrac{9}{10}=\dfrac{3}{2}\)

a) \(\dfrac{3}{4}-\dfrac{1}{8}=\dfrac{6}{8}-\dfrac{1}{8}=\dfrac{6-1}{8}=\dfrac{5}{8}\)

b) \(\dfrac{2}{6}-\dfrac{5}{18}=\dfrac{6}{18}-\dfrac{5}{18}=\dfrac{6-5}{18}=\dfrac{1}{18}\)

c) \(\dfrac{2}{5}-\dfrac{3}{20}=\dfrac{8}{20}-\dfrac{3}{20}=\dfrac{8-3}{20}=\dfrac{5}{20}=\dfrac{1}{4}\)

a) ( 42- 6) : 1/2 + 7/6

= 36 : 1/2 + 7/6

= 72 + 7/6

= 439/6

b) 18/5 - 2/7 + 1/3

= 383/105

a) = ( 42 - 6) : 1/2 + 7/6 

= 36 : 1/2 + 7/6

= 72 + 7/6

= 439/6

b) = 18/5 - 2/7 + 1/3

= 116/35 + 1/3

= 383/105

\(a.=\left(42-6\right):\dfrac{1}{2}+\dfrac{7}{6}\)

\(=36:\dfrac{1}{2}+\dfrac{7}{6}\)

\(=\)\(72+\dfrac{7}{6}\)

\(=\dfrac{439}{6}\)

\(=\dfrac{1}{2}+\dfrac{5}{6}-\dfrac{1}{2}-\dfrac{5}{6}+2022=2022\)

2022

\(\dfrac{1}{2}-\dfrac{35}{-42}+2022-\dfrac{18}{36}-\dfrac{5}{6}\\ =\dfrac{1}{2}-\dfrac{-5}{6}+2022-\dfrac{1}{2}-\dfrac{5}{6}\\ =\left(\dfrac{1}{2}-\dfrac{1}{2}\right)-\left(\dfrac{-5}{6}+\dfrac{5}{6}\right)+2022\\ =0-0+2022\\ =0+2022\\ =2022\)

TL
\(\frac{3}{15}\)-\(\frac{5}{35}\)=\(\frac{1}{5}\)\(-\frac{1}{7}\)=\(\frac{2}{35}\)

\(\frac{18}{27}\)-\(\frac{2}{6}\)=\(\frac{2}{3}\)-\(\frac{1}{3}\)=\(\frac{1}{3}\)

nha bn

HT

ai đúng mình tích

\(a,=\dfrac{9}{12}-\dfrac{7}{12}-\dfrac{8}{12}=-\dfrac{1}{2}\\ b,=\dfrac{95}{6}+\dfrac{17}{18}-\dfrac{5}{12}=\dfrac{589}{36}\)

SAO THỔ

\(a,12.\dfrac{-7}{11}.\dfrac{5}{6}.\dfrac{22}{7}=\left(12.\dfrac{5}{6}\right)\left(\dfrac{-7}{11}.\dfrac{22}{7}\right)=10.\left(-2\right)=-20\\ b,\dfrac{-8}{15}.\dfrac{7}{9}.\dfrac{5}{8}.\left(-18\right)=\left(\dfrac{-8}{15}.\dfrac{5}{8}\right)\left[\dfrac{7}{9}.\left(-18\right)\right]=\dfrac{-1}{3}.\left(-14\right)=\dfrac{14}{3}\)

a) 12.−711.56.227= (12.56)(−711.227)= 10.(−2)= −20.

b) −815.79.58.(−18)= (−815.58)[79.(−18)]= −13.(−14)= 143.