`1 1/5 + 5/9 + 4/5 + 5/9`
`=6/5 + 5/9 + 4/5 + 5/9`
`=(6/5 + 4/5) + (5/9 + 5/9)`
`=10/5 + 10/9`
`=2 + 10/9`
`=18/9 + 10/9`
`=28/9`
________________________
`7/15 . 11/13 + 7/15 . 2/13 + 8/15`
`= [7/15 . (11/13 + 2/13)] + 8/15`
`= [7/15 . ((11+2)/13)] + 8/15`
`=7/15 . 13/13 + 8/15`
`=7/15 .1 + 8/15`
`=7/15 + 8/15`
`=15/15`
`=1`
____________________________
`9/20 + 7/15 + 1/12`
`=(9/20 + 7/15) + 1/12`
`=(27/60 + 28/60) + 1/12`
`=55/60 + 1/12`
`=11/12 + 1/12`
`=12/12`
`=1`
_______________________
`(7/20 - 4/15) : (7/12 - 5/18)`
`=(21/60 - 16/60) : (21/36 - 10/36)`
`=` \(\left(\dfrac{21-16}{60}\right):\left(\dfrac{21-10}{36}\right)\)
`=1/12 : 11/36`
`=1/12 . 36/11`
`=3/11`
a,\(1\dfrac{1}{5}+\dfrac{5}{9}+\dfrac{4}{5}+\dfrac{5}{9}\)
\(=\dfrac{6}{5}+\dfrac{5}{9}+\dfrac{4}{5}+\dfrac{5}{9}\)
\(=\left(\dfrac{6}{5}+\dfrac{4}{5}\right)+\left(\dfrac{5}{9}+\dfrac{5}{9}\right)\)
\(=2+\dfrac{10}{9}\)
\(=\dfrac{18}{9}+\dfrac{10}{9}=\dfrac{28}{9}\)
\(b,\dfrac{7}{15}.\left(\dfrac{11}{13}+\dfrac{2}{13}\right)+\dfrac{8}{15}\)
\(=\dfrac{7}{15}.1+\dfrac{8}{15}=\dfrac{7}{15}+\dfrac{8}{15}\)
\(=1\)
\(c,\dfrac{27}{60}+\dfrac{28}{60}+\dfrac{5}{60}=\dfrac{60}{60}=1\)
\(d,\left(\dfrac{21}{60}-\dfrac{16}{60}\right):\left(\dfrac{21}{36}-\dfrac{10}{36}\right)\)
\(=\dfrac{1}{12}:\dfrac{1}{36}=\dfrac{1}{12}.\dfrac{36}{1}\)
\(=\dfrac{36}{12}=3\)
