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a/7/9(1/4+3/4)=7/9.1=7/9
b/13/9(16/5-14/5+3/5)=13/9.1=13/9
34cm=34/100m
524mm=524/1000m
70mm=70/1000=7/100m
a/7/9(1/4+3/4)=7/9.1=7/9
b/13/9(16/5-14/5+3/5)=13/9.1=13/9
34cm=34/100m
524mm=524/1000m
70mm=70/1000=7/100m
![](https://rs.olm.vn/images/avt/0.png?1311)
Ta có:
\(\frac{1}{3\times4}+\frac{1}{4\times5}+\frac{1}{5\times6}+.....+\frac{1}{14\times15}=\frac{4-3}{3\times4}+\frac{5-4}{4\times5}+\frac{6-5}{6\times5}+...+\frac{15-14}{14\times15}\)
\(=\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+...+\frac{1}{14}-\frac{1}{15}=\frac{1}{3}-\frac{1}{15}=\frac{4}{15}\)
Do đó: \(\frac{4}{15}=\frac{x}{30}\)
\(x=\frac{4}{15}\times30=8\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\frac{1}{3\times4}+\frac{1}{4\times5}+\frac{1}{5\times6}+...+\frac{1}{14\times15}=\frac{x}{30}\)
\(\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{5}+...+\frac{1}{14}-\frac{1}{15}=\frac{x}{30}\)
\(\frac{1}{3}-\frac{1}{15}=\frac{x}{30}\)
\(\frac{4}{15}=\frac{x}{30}\)
\(\Rightarrow4\times30=15\times x\)
\(120=15\times x\)
\(x=120\div15\)
\(x=8.\)
\(\frac{1}{3.4}+\frac{1}{4.5}+\frac{1}{5.6}+...+\frac{1}{14.15}=\frac{x}{30}\)
\(\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+...+\frac{1}{14}-\frac{1}{15}=\frac{x}{30}\)
\(\frac{1}{3}-\frac{1}{15}=\frac{x}{30}\)
\(\frac{5}{15}-\frac{1}{15}=\frac{x}{30}\)
\(\frac{4}{15}=\frac{x}{30}\)
\(\frac{8}{30}=\frac{x}{30}\)
\(x=8\)
hok tốt!!
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\frac{14}{6}+\frac{1}{3}+\frac{14}{14}+\frac{14}{9}+\frac{7}{15}+\frac{6}{4}\)
\(=\frac{14}{6}+\frac{1}{3}+\frac{14}{9}+\frac{7}{15}+\frac{14}{14}+\frac{6}{4}\)
\(=\frac{42+6+28}{18}+\frac{7}{15}+\frac{2}{2}+\frac{3}{2}\)
\(=\frac{76}{18}+\frac{7}{15}+\frac{5}{2}\)
\(=\frac{76}{18}+\frac{5}{2}+\frac{7}{15}\)
\(=\frac{76+45}{18}+\frac{7}{15}\)
\(=\frac{121}{18}+\frac{7}{15}\)
\(=\frac{605+42}{90}\)
\(=\frac{647}{90}\)
\(\frac{14}{6}+\frac{1}{3}+\frac{14}{14}+\frac{14}{9}+\frac{7}{15}+\frac{6}{4}\)
\(=(\frac{7}{3}+\frac{1}{3})+1+(\frac{14}{9}+\frac{7}{15})+\frac{3}{2}\)
\(=\frac{8}{3}+1+\frac{91}{45}+\frac{3}{2}\)
\(=2+\frac{2}{3}+1+2+\frac{1}{45}+1+\frac{1}{2}\)
\(=\left(\frac{2}{3}+\frac{1}{45}+\frac{1}{2}\right)+\left(2+1+2+1\right)\)
\(=1+\frac{17}{90}+6\)
\(=7+\frac{17}{90}\)
\(=7\frac{17}{90}\)
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= 2/21
=9/5
=37/6:\(6\frac{1}{6}\)
=79/20: tự đổi nhe bạn
=3/5__________-
\(\frac{4}{15}x\frac{5}{14}=\frac{4x5}{15x14}=\frac{2x1}{3x7}=\frac{2}{21}\)
\(\frac{3}{4}:\frac{5}{12}=\frac{3}{4}x\frac{12}{5}=\frac{3x12}{4x5}=\frac{3x3}{1x5}=\frac{9}{5}=1,8\)
\(\frac{7}{2}+\frac{8}{3}=\frac{7x3}{2x3}+\frac{8x2}{3x2}=\frac{21}{6}+\frac{16}{6}=\frac{21+16}{6}=\frac{37}{6}\)
m= 660/17