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b)\(\left(\dfrac{13}{21}\times\dfrac{7}{8}-\dfrac{12}{21}\times\dfrac{7}{8}\right)\times12\)
=\(\left(\dfrac{7}{8}\times\left(\dfrac{13}{21}-\dfrac{12}{21}\right)\right)\times12\)
=\(\left(\dfrac{7}{8}\times\dfrac{1}{21}\right)\times12\)
=\(\dfrac{7}{16}\)
c)\(\dfrac{7}{11}+\dfrac{3}{4}+\dfrac{4}{11}+\dfrac{8}{17}+\dfrac{1}{4}+\dfrac{18}{34}\)
= \(\left(\dfrac{7}{11}+\dfrac{4}{11}\right)+\left(\dfrac{3}{4}+\dfrac{1}{4}\right)+\dfrac{8}{17}+\dfrac{9}{17}\)
= 1 + 1 + \(\left(\dfrac{8}{17}+\dfrac{9}{17}\right)\)
= 2 + 1
= 3
xet tu so : 1,13,25,.....89,97
co tat cac tu so la : ( 97-1);12+1=9(tu so)
tong tat ca tu so la: ( 97+1)x9;2=441
vay tong do la : 441/1000
\(A=\frac{65+891+135+909}{731-47+69-253}\)
\(A=\frac{65+135+891+909}{731+69-47-253}\)
\(A=\frac{\left(65+135\right)+\left(891+909\right)}{\left(731+69\right)-\left(47+253\right)}\)
\(A=\frac{200+1800}{800-300}\)
\(A=\frac{2000}{500}=4\)
A = \(\frac{65+891+135+909}{731-47+69-253}\)
A = \(\frac{\left(65+135\right)+\left(891+909\right)}{\left(731+69\right)-\left(47+253\right)}\)
A = \(\frac{200+1800}{800-300}\)
A = \(\frac{2000}{500}\)
A = 4
\(\frac{13}{8}-\frac{375}{1000}\)
\(=\frac{13}{8}-\frac{3}{8}\)
\(=\frac{10}{8}\)
\(=\frac{5}{4}\)
Chúc bạn học tốt !!!