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28 x 34 - 17 x 56 + 1000
= 28 x 34 - 17 x 2 x 28 + 1000
= 28 x 34 - 34 x 28 + 1000
= 28 x (34 - 34) + 1000
= 28 x 0 + 1000
= 0 + 1000 = 1000
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\(\frac{24}{36}:\frac{8}{9}=\frac{24}{36}\cdot\frac{9}{8}=\frac{24\cdot9}{36\cdot8}=\frac{216}{288}=\frac{3}{4}\)
\(\frac{32}{45}-\frac{7}{30}=\frac{64}{90}-\frac{21}{90}=\frac{43}{90}\)
\(\frac{3}{10}+\frac{4}{7}+\frac{6}{14}+\frac{4}{20}=\frac{42}{140}+\frac{80}{140}+\frac{60}{140}+\frac{28}{140}=\frac{210}{140}=\frac{3}{2}\)
\(\frac{17}{25}\cdot\frac{11}{28}+\frac{34}{50}\cdot\frac{17}{28}=\frac{187}{700}+\frac{289}{700}=\frac{476}{700}=\frac{17}{25}\)
\(\frac{1}{3\cdot4}+\frac{1}{4\cdot5}+\frac{1}{5\cdot6}+...+\frac{1}{11\cdot12}=\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+...+\frac{1}{11}-\frac{1}{12}=\frac{1}{3}-\frac{1}{12}=\frac{1}{4}\)
17/25
\(\frac{17}{25}\times\frac{11}{28}+\frac{34}{50}\times\frac{17}{28}=\frac{187}{700}+\frac{289}{700}=\frac{17}{25}\)