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a: \(=\left(\dfrac{4}{9}+\dfrac{5}{9}\right)+\left(\dfrac{1}{8}+\dfrac{7}{8}\right)=1+1=2\)
b: \(=\left(\dfrac{1}{6}+\dfrac{4}{6}+\dfrac{7}{6}\right)+\left(\dfrac{5}{12}+\dfrac{7}{12}\right)=2+1=3\)
Ta có thể đổi chỗ các phân số :
A)(7/12+5/12)+(4/9+1/3)+2=12/12+7/9+2=1+2+7/9=3+7/9=34/9
B)6/5*(3/8+5/8)-4/5=6/5*1-4/5=6/5-4/5=2/5
a] 4/12 ; 5/12 ; 11/2 ; 1/4
b] 1 ; 9/12; 12/5 ; 11/3
c] 8/21; 6/11;8/7
d] 2/3 ;2/7 15/2
a]1/3 5/12 11/2 1/4
b]1 3/4 12/5 33/9
c]8/21 6/11 8/7
d]2/3 2/7 15/2
\(\dfrac{2}{5}+\dfrac{2}{3}+\dfrac{2}{4}\)
= \(\dfrac{24}{60}\) + \(\dfrac{40}{60}\) + \(\dfrac{30}{60}\)
= \(\dfrac{64}{60}\) + \(\dfrac{30}{60}\)
= \(\dfrac{47}{30}\)
\(\dfrac{2}{6}+\dfrac{3}{12}\)
= \(\dfrac{4}{12}\) + \(\dfrac{3}{12}\)
= \(\dfrac{7}{12}\)
\(\dfrac{5}{6}\) + \(\dfrac{1}{3}\)
= \(\dfrac{5}{6}\) + \(\dfrac{2}{6}\)
= \(\dfrac{7}{6}\)
\(\dfrac{1}{3}\) + \(\dfrac{5}{12}\) + \(\dfrac{5}{6}\)
= \(\dfrac{4}{12}\) + \(\dfrac{5}{12}\) + \(\dfrac{10}{12}\)
= \(\dfrac{9}{12}\) + \(\dfrac{10}{12}\)
= \(\dfrac{19}{12}\)
\(\dfrac{5}{8}\) + \(\dfrac{4}{7}\)
= \(\dfrac{35}{56}\) + \(\dfrac{32}{56}\)
= \(\dfrac{67}{56}\)
\(\dfrac{7}{3}\) + \(\dfrac{8}{7}\)
= \(\dfrac{49}{21}\) + \(\dfrac{24}{21}\)
= \(\dfrac{73}{21}\)
\(\dfrac{1}{5}+\dfrac{5}{35}\)
= \(\dfrac{7}{35}\) + \(\dfrac{5}{35}\)
= \(\dfrac{12}{35}\)
câu a) lấy mẫu số chung cộng với nhau
câu b) lấy 1 để ngoài nhân r 1/2-1/3 rồi tương tự
\(\dfrac{1}{2}\times\dfrac{3}{4}:\dfrac{6}{5}=\dfrac{3}{8}:\dfrac{6}{5}=\dfrac{5}{16}\)
\(\dfrac{2}{3}+\dfrac{1}{6}:\dfrac{7}{12}=\dfrac{2}{3}+\dfrac{2}{7}=\dfrac{14}{21}+\dfrac{6}{21}=\dfrac{20}{21}\)
\(8\times\dfrac{3}{5}:\dfrac{12}{5}=\dfrac{24}{5}:\dfrac{12}{5}=2\)
\(\dfrac{4}{9}+\dfrac{3}{4}-\dfrac{1}{3}=\dfrac{16}{36}+\dfrac{27}{36}-\dfrac{12}{36}=\dfrac{31}{36}\)
\((\)125-120\()\)x45
5x45=225
\(\dfrac{30x25x7x8}{75x8x12x14}\)=\(\dfrac{10\cdot1\cdot7\cdot1}{1\cdot1\cdot1\cdot12\cdot2}\)=\(\dfrac{70}{24}\)
\(\dfrac{1}{4}+\dfrac{1}{6}+\dfrac{7}{4}+\dfrac{5}{12}+\dfrac{5}{6}+\dfrac{7}{12}\)
\(=\left(\dfrac{1}{4}+\dfrac{7}{4}\right)+\left(\dfrac{1}{6}+\dfrac{5}{6}\right)+\left(\dfrac{5}{12}+\dfrac{7}{12}\right)\)
=2+1+1
=4
1/4 + 1/6 + 7/4 + 5/12 + 5/6 + 7/12
=(5/6+ 1/6) + (7/4 + 1/4) + (5/12 + 7/12)
= 6/6 + 8/4 + 12/12
= 1 + 2 + 1
= 4