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Câu 1 : 1305 ; 6805
Câu 2 :
a) = 1407 dm2
b) = 506 giây
c) = 3 tấn 2400 kg
Câu 3 :
\(=15\times\dfrac{3}{5}=9\)
\(a,\dfrac{2}{7}+\dfrac{1}{4}=\dfrac{8}{28}+\dfrac{7}{28}=\dfrac{15}{28}\\ b,\dfrac{3}{5}+\dfrac{3}{8}=\dfrac{3.8}{5.8}+\dfrac{3.5}{5.8}=\dfrac{6}{5}\\ c,=\dfrac{4.3}{9.3}+\dfrac{10}{27}=\dfrac{12+10}{27}=\dfrac{22}{27}\\ d,=\dfrac{2.3}{3.3}+\dfrac{7}{9}=\dfrac{6+7}{9}=\dfrac{13}{9}\\ e,=\dfrac{5.5}{12.5}+\dfrac{7.4}{15.4}=\dfrac{25+28}{60}=\dfrac{53}{60}\)
\(\dfrac{2}{7}+\dfrac{1}{4}=\dfrac{8}{28}+\dfrac{7}{28}=\dfrac{15}{28};\dfrac{3}{5}+\dfrac{3}{8}=\dfrac{24}{40}+\dfrac{15}{40};\dfrac{4}{9}+\dfrac{10}{27}=\dfrac{12}{27}+\dfrac{10}{27}=\dfrac{22}{27};\dfrac{2}{3}+\dfrac{7}{9}=\dfrac{18}{27}+\dfrac{21}{27}=\dfrac{39}{27};\dfrac{5}{12}+\dfrac{7}{15}=\dfrac{75}{180}+\dfrac{84}{180}=\dfrac{159}{180}\)
`1) 11/12xx28/13-11/12xx15/13`
`=11/12xx(28/13-15/13)`
`=11/12xx13/13=11/12`
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`2)x+653=87xx11`
`x+653=957`
`x=957-653`
`x=304`
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`3)70 000 + 800 + 20 + 9 =70 829`
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`4)` Độ dài `1 cm` trên bản đồ ứng với độ dài thật là:
`1 : 1 xx 500 = 500 (cm)`
a: \(=\left(\dfrac{21}{11}+\dfrac{12}{11}\right)+\left(-\dfrac{9}{19}-\dfrac{3}{19}-\dfrac{6}{19}\right)=3-\dfrac{18}{19}=\dfrac{57}{19}-\dfrac{18}{19}=\dfrac{39}{19}\)
b: \(=\left(\dfrac{2}{3}+\dfrac{4}{3}\right)+\left(\dfrac{3}{4}+\dfrac{7}{4}\right)+\left(\dfrac{4}{5}+\dfrac{16}{5}\right)=2+4+\dfrac{5}{2}=6+\dfrac{5}{2}=\dfrac{17}{2}\)
a,\(\dfrac{2}{5}+\dfrac{1}{10}=\dfrac{4}{10}+\dfrac{1}{10}=\dfrac{5}{10}=\dfrac{1}{2}\)
\(b,3-\dfrac{1}{2}=\dfrac{3}{1}-\dfrac{1}{2}=\dfrac{6}{2}-\dfrac{1}{2}=\dfrac{5}{2}\)
\(c,\dfrac{7}{12}x\dfrac{12}{21}=\dfrac{1}{3}\)
\(d,4:\dfrac{2}{3}=\dfrac{4}{1}:\dfrac{2}{3}=\dfrac{4}{1}x\dfrac{3}{2}=\dfrac{6}{1}=6\)
a) \(\dfrac{2}{5}+\dfrac{1}{10}=\dfrac{4}{10}+\dfrac{1}{10}=\dfrac{5}{10}=\dfrac{1}{2}\)
b) \(3-\dfrac{1}{2}=\dfrac{6}{2}-\dfrac{1}{2}=\dfrac{5}{2}\)
c) \(\dfrac{7}{12}\times\dfrac{12}{21}=\dfrac{7}{21}=\dfrac{1}{3}\)
d) \(4:\dfrac{2}{3}=4\times\dfrac{3}{2}=6\)