tính bằng cách thuận tiện 13/60+19/30+11/60
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13/19 x 23/11 - 13/19 x 8/11 - 13/19 x 4/11
= 13/19 x (23/11 - 8/11 - 4/11)
= 13/19 x 1
= 13/19
\(\dfrac{13}{19}\times\dfrac{23}{11}-\dfrac{13}{19}\times\dfrac{8}{11}-\dfrac{13}{19}\times\dfrac{4}{11}\\ =\dfrac{13}{19}\times\left(\dfrac{23}{11}-\dfrac{8}{11}-\dfrac{4}{11}\right)\\ =\dfrac{13}{19}\times1=\dfrac{13}{19}\)

\(\dfrac{3}{5}+\dfrac{6}{11}+\dfrac{7}{13}+\dfrac{2}{5}+\dfrac{16}{11}+\dfrac{19}{13}\\ =\left(\dfrac{3}{5}+\dfrac{2}{5}\right)+\left(\dfrac{6}{11}+\dfrac{16}{11}\right)+\left(\dfrac{7}{13}+\dfrac{19}{13}\right)\\ =\dfrac{5}{5}+\dfrac{22}{11}+\dfrac{26}{13}\\ =1+2+2\\ =5\)

19/11 + ( 8/13 + 3/11 )
=( 19/11+3/11 )+8/13
=2+8/13
=26/13+8/13
=34/13

10 x 60 + 10 x 70 - 10 x 30
= ( 10 x 60 ) + ( 10 x 70 ) - ( 10 x 30 )
= 160 + 170 - 130
= 160 + 140
= 200
tính bằng cách thuận tiện nhất
a,4/15 x 7/8 + 4/15 x 2/9
b, 13/29 x 23/11 -13/19 x 8/11 - 13/19 x 4/11



\(\frac{13}{19}\times\frac{23}{11}-\frac{13}{19}\times\frac{8}{11}-\frac{13}{19}\times\frac{4}{11}\)
\(=\frac{13}{19}\times\left(\frac{23}{11}-\frac{8}{11}-\frac{4}{11}\right)\)
\(=\frac{13}{19}\times1\)
\(=\frac{13}{19}\)
13/19 x 23/11 - 13/19 x 8/11 - 13/19 x 4/11
= 13/19 x (23/11 - 8/11 - 4/11)
= 13/19 x 1
= 13/19

50-51+40-41+30-31+60
=-1+(-1)+(-1)+60
=-3+60
=57

(20+10)-(11+19)+(12+18)-(13+17)+(14+16)-15
=30-30+30-30-15+30
=15
10-11+12-13+14-15+16-17+18-19+20
= (10+20)+(-11-19)+(12+18)+(-13-17)+(14+16)-15
= 30-30+30-30+30-15
= 15
\(\frac{13}{60}\) + \(\frac{19}{30}\) + \(\frac{11}{60}\)
= (\(\frac{13}{60}+\frac{11}{60})\) + \(\frac{19}{30}\)
= \(\frac{12}{30}\) + \(\frac{19}{30}\)
= \(\frac{31}{30}\)
\(\dfrac{13}{60}+\dfrac{19}{30}+\dfrac{11}{60}\)
\(=\dfrac{13+11}{60}+\dfrac{19}{30}\)
\(=\dfrac{24}{60}+\dfrac{19}{30}=\dfrac{12}{30}+\dfrac{19}{30}=\dfrac{31}{30}\)