Mik ko viết được phân số bạn thông cảm :'(

$\dfrac{1}{2}$ + $\dfrac{5}{6}$ + $\dfrac{11}{22}$ + $\dfrac{19}{20}$ + $\dfrac{29}{30}$ + $\dfrac{41}{42}$ + $\dfrac{55}{56}$ + $\dfrac{71}{72}$ + $\dfrac{89}{90}$

= ( $\dfrac{1}{2}$ + $\dfrac{1}{2}$ ) + ( $\dfrac{35}{42}$ + $\dfrac{41}{42}$ ) + $\dfrac{19}{20}$ + $\dfrac{29}{30}$ + $\dfrac{55}{56}$  + $\dfrac{71}{72}$ + $\dfrac{89}{90}$

= 1 + $\dfrac{38}{21}$ + $\dfrac{19}{20}$ + $\dfrac{29}{30}$ + $\dfrac{55}{56}$ + $\dfrac{71}{72}$ + $\dfrac{89}{90}$

= $\dfrac{59}{21}$ + ( $\dfrac{57}{60}$ + $\dfrac{58}{60}$ ) + $\dfrac{55}{56}$ + $\dfrac{71}{72}$ + $\dfrac{89}{90}$

= $\dfrac{59}{21}$ + $\dfrac{115}{60}$ + ( $\dfrac{3960}{4032}$ + $\dfrac{3976}{4032}$ ) + $\dfrac{89}{90}$ 

= $\dfrac{59}{21}$ + $\dfrac{115}{60}$ + $\dfrac{62}{63}$ + $\dfrac{89}{90}$

= ( $\dfrac{177}{63}$ + $\dfrac{62}{63}$ ) + ( $\dfrac{345}{180}$ + $\dfrac{178}{180}$ )

= $\dfrac{239}{63}$ + $\dfrac{523}{180}$

= $\dfrac{43020}{11340}$ + $\dfrac{32949}{11340}$

= $\dfrac{8441}{1260}$