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\(\frac{1}{9\cdot10}+\frac{2}{10\cdot12}+\frac{3}{12\cdot15}+\frac{4}{15\cdot19}+\frac{5}{19\cdot24}+\frac{6}{24\cdot30}
\)
\(=\frac{1}{9}-\frac{1}{10}+\frac{1}{10}-\frac{1}{12}+\frac{1}{12}-\frac{1}{15}+\frac{1}{15}-\frac{1}{19}+\frac{1}{19}-\frac{1}{24}+\frac{1}{24}-\frac{1}{30}\)
\(=\frac{1}{9}-\frac{1}{30}\)
\(=\frac{10}{90}-\frac{3}{90}\)
\(=\frac{7}{90}\)
\(\frac{15}{24}-\frac{2}{15}=\frac{5}{8}-\frac{2}{15}=\frac{75}{120}-\frac{16}{120}=\frac{59}{120}\)
4 : 9 = \(\dfrac{4}{9}\) 8 : 11 =\(\dfrac{8}{11}\) 7 : 15 =\(\dfrac{7}{15}\)
15 : 5 = \(\dfrac{15}{5}=\dfrac{3}{1}\) 63 : 21 =\(\dfrac{63}{21}\) 45 : 9 =\(\dfrac{45}{9}=\dfrac{5}{1}\)
6 : 18 = \(\dfrac{6}{18}=\dfrac{1}{3}\) 144 : 24 =\(\dfrac{244}{24}\) 7 =\(\dfrac{7}{1}\)
15 = \(\dfrac{15}{1}\) 10 = \(\dfrac{10}{1}\) 0 =\(\dfrac{0}{1}\)
\(4:9=\dfrac{4}{9};15:5=\dfrac{15}{5}=3;6:18=\dfrac{6}{18}=\dfrac{1}{3}\\ 15=\dfrac{15}{1};8:11=\dfrac{8}{11};63:21=\dfrac{63}{21}=3;144:24=\dfrac{144}{24};10=\dfrac{10}{1}\\ 7:15=\dfrac{7}{15};45:9=\dfrac{45}{9}=5;7=\dfrac{7}{1};0=0\)
`24/15 xx 2/7 + 7/5 xx 2/7`
`= 2/7 xx (24/15 + 7/5)`
`= 2/7 xx 3`
`= 6/7`
a, = 15 x (3+7) + 15 = 15 x 10 + 15 = 150 + 15 = 165
b, = 24 x 18 - 24 x 8 + 24 = 24 x (18-8) + 24 = 24 x 10 + 24 = 240 + 24 = 264
k mk nha
a,15*3+15*7+15
=15*(3+7)
=15*10
=150
b,24*18-24*7
=24*(18-7)
=24*11
=264
tk cho mk nha^-^
a \(x=\dfrac{2}{15}:\dfrac{4}{15}\)
\(x=\dfrac{2}{15}\times\dfrac{15}{4}\)
\(x=\dfrac{1}{2}\)
b \(\dfrac{7}{24}+x=\dfrac{7}{4}\)
\(x=\dfrac{7}{4}-\dfrac{7}{24}\)
\(x=\dfrac{42}{24}-\dfrac{7}{24}\)
\(x=\dfrac{35}{24}\)
5/4
\(\dfrac{15}{24}+2=\dfrac{15}{24}+\dfrac{48}{24}=\dfrac{63}{24}=\dfrac{21}{8}\)