câu 20: C

bài 5:\(\dfrac{9}{15}\);\(\dfrac{11}{15}\);\(\dfrac{15}{15}\);\(\dfrac{14}{13}\)

bài 10:

\(\dfrac{25}{12}\)> 1

\(\dfrac{1999}{2000}\)<1

=> \(\dfrac{25}{12}>\dfrac{1999}{2000}\)

bài 15:

Chiều dài của miếng đất hcn đó là : 19x3= 57 m

Cạnh miếng đất hình vuông là: (19+57):2=38 m

Diện tích miếng đất hình vuông là : 38 x 38= 1444 \(^{m^2}\)\

Chúc bạn học tốt! Có chỗ nào không hiểu hỏi lại mình nhá

=3/2-8/21x16/14=3/2-64/147=313/294

\(\dfrac{30}{20}-\dfrac{8}{21}x\dfrac{16}{14}\)

= \(\dfrac{30}{20}-\dfrac{64}{147}\)

= \(\dfrac{313}{294}\)

313/294

313/294

\(\dfrac{15}{16}:\dfrac{5}{8}\times\dfrac{3}{4}\)

\(=\dfrac{15}{16}\times\dfrac{8}{5}\times\dfrac{3}{4}\)

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

\(=\dfrac{9}{8}\)

_________________

\(\dfrac{21}{4}\times\dfrac{16}{14}\times\dfrac{1}{2}\times\dfrac{8}{3}\)

\(=6\times\dfrac{4}{3}\)

\(=8\)

\(=28\left(\dfrac{3}{14}-\dfrac{13}{21}-\dfrac{29}{42}\right)-8\\ =28\cdot\dfrac{-23}{21}-8=-\dfrac{92}{3}-8=-\dfrac{116}{3}\)

\(C=\dfrac{3}{14}:\dfrac{1}{28}-\dfrac{13}{21}:\dfrac{1}{28}-\dfrac{29}{42}:\dfrac{1}{28}-8\)

\(=28\left(\dfrac{3}{14}-\dfrac{13}{21}-\dfrac{29}{42}\right)-8\)

\(=28\left(\dfrac{9}{42}-\dfrac{26}{42}-\dfrac{29}{42}\right)-8\)

\(=28\cdot\dfrac{-46}{42}-8\)

\(=\dfrac{-116}{3}\)

c: \(\dfrac{3}{14}:\dfrac{1}{28}-\dfrac{13}{21}:\dfrac{1}{28}\)

\(=28\left(\dfrac{3}{14}-\dfrac{13}{21}\right)\)

\(=28\cdot\left(\dfrac{9}{42}-\dfrac{26}{42}\right)\)

\(=28\cdot\dfrac{-17}{42}=\dfrac{-34}{3}\)

\(=\dfrac{7}{6}\cdot\dfrac{3}{14}-\dfrac{4}{7}\cdot\dfrac{21}{8}+1=\dfrac{1}{4}-\dfrac{3}{2}+1=\dfrac{1}{4}-\dfrac{6}{4}+\dfrac{4}{4}=-\dfrac{1}{4}\)

\(\dfrac{-8}{13}+\dfrac{-7}{17}+\dfrac{21}{13}\le x\le\dfrac{-9}{14}+3+\dfrac{5}{-14}\)

=> \(\dfrac{10}{17}\le x\le2\)

=> \(\dfrac{10}{17}\le\dfrac{17x}{17}\le\dfrac{34}{17}\)

=> 10 \(\le17x\le34\)
=> x = 1; 2 (thỏa mãn)
@Khánh Linh

C

Chọn C

C