\(4,7\div0,25+5,3\times4\)

\(=18,8+21,2\)

\(=40\)

\(3\times\left(a-2\right)+150=240\)

\(3\times\left(a-2\right)=90\)

\(a-2=30\)

\(a=32\)

\(\dfrac{1}{9}+a+\dfrac{7}{12}=\dfrac{17}{18}\)

\(\dfrac{1}{9}+a=\dfrac{13}{36}\)

\(a=\dfrac{1}{4}\)

\(\left(\dfrac{1}{2}\times\dfrac{1}{3}+\dfrac{1}{3}\times\dfrac{1}{4}+\dfrac{1}{4}\times\dfrac{1}{5}+\dfrac{1}{5}\times\dfrac{1}{6}+\dfrac{1}{6}\times\dfrac{1}{7}+\dfrac{1}{7}\times\dfrac{1}{8}\right)\times a=\dfrac{9}{16}\)

\(\left(\dfrac{1}{2\times3}+\dfrac{1}{3\times4}+\dfrac{1}{4\times5}+\dfrac{1}{5\times6}+\dfrac{1}{6\times7}+\dfrac{1}{7\times8}\right)\times a=\dfrac{9}{16}\)

\(\left(\dfrac{1}{2}-\dfrac{1}{8}\right)\times a=\dfrac{9}{16}\)

\(\dfrac{3}{8}\times a=\dfrac{9}{16}\)

\(a=\dfrac{3}{2}\)

30 em cuốc trong 1 giờ được:

180 : 2 = 90 mét vuông

1 em cuốc trong 1 giờ được:

90 : 30 = 30 (m2)

50 em cuốc trong 1 giờ được là:

30 x 50 = 1500 (m2)

50 em cuốc trong 3 giờ được:

1500 x 3 = 4500 (m2)

5 là nam nha viết nhầm

Đổi:  \(25\dfrac{15}{100}=\dfrac{2515}{100}=25,15\)  tạ 

=> 25 tạ 15 kg

=> \(25\dfrac{15}{100}\)  tạ = 25 tạ 15 kg

\(3\dfrac{2}{3}\div1\dfrac{1}{4}=\dfrac{11}{3}\div\dfrac{5}{4}=\dfrac{11}{3}\times\dfrac{4}{5}=\dfrac{44}{15}\)

\(5\dfrac{1}{7}.2\dfrac{3}{5}=\dfrac{36}{7}.\dfrac{13}{5}=\dfrac{468}{35}\)

`@` `\text {Ans}`

`\downarrow`

`a)`

\(4\dfrac{2}{3}-2\dfrac{3}{4}\)

`=`\(\dfrac{3\times4+2}{3}-\dfrac{4\times2+3}{4}\)

`=`\(\dfrac{14}{3}-\dfrac{11}{4}=\dfrac{23}{12}\)

\(4\dfrac{2}{3}=\dfrac{14}{3}\)

\(2\dfrac{3}{4}=\dfrac{11}{4}\)

=> \(\dfrac{14}{3}-\dfrac{11}{4}=\dfrac{56}{12}-\dfrac{33}{12}=\dfrac{23}{12}\)

\(\dfrac{1}{3}+\dfrac{5}{6}\cdot\left(x-\dfrac{11}{5}\right)=\dfrac{3}{4}\)

\(\dfrac{5}{6}\cdot\left(x-\dfrac{11}{5}\right)=\dfrac{3}{4}-\dfrac{1}{3}\)

\(\dfrac{5}{6}\cdot\left(x-\dfrac{11}{5}\right)=\dfrac{5}{12}\)

\(x-\dfrac{11}{5}=\dfrac{5}{12}\cdot\dfrac{6}{5}\)

\(x-\dfrac{11}{5}=\dfrac{1}{2}\)

\(x=\dfrac{1}{2}+\dfrac{11}{5}\)

\(x=\dfrac{27}{10}\)

\(\dfrac{5}{6}\left(x-\dfrac{11}{5}\right)=\dfrac{3}{4}-\dfrac{1}{3}\)

\(\dfrac{5}{6}\left(x-\dfrac{11}{5}\right)=\dfrac{5}{12}\)

\(x-\dfrac{11}{5}=\dfrac{5}{12}:\dfrac{5}{6}\)

\(x-\dfrac{11}{5}=\dfrac{1}{2}\)

\(x=\dfrac{1}{2}+\dfrac{11}{5}=\dfrac{27}{10}\)

18 x 125 + 18 x 450 + 18 x 425 

= 18 x ( 125 + 450 + 425 ) 

= 18 x 1000 

= 1800

☹

`@` `\text {Ans}`

`\downarrow`

`a)`

\(3\dfrac{1}{2}\)\(+1\dfrac{1}{15}\)

`=`\(\dfrac{2\times3+1}{2}+\dfrac{1\cdot15+1}{15}\)

`=`\(\dfrac{7}{2}+\dfrac{16}{15}\)

`= 137/30`