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a,2/9+1/6=7/18
b,5/6-4/7=11/42
c,3/8.6/15=3/20
d,7/12:4/7=49/48
e,4/7:3=4/21
b) 
d) 
a: \(\dfrac{3}{8}+\dfrac{7}{8}=\dfrac{3+7}{8}=\dfrac{10}{8}=\dfrac{5}{4}\)
b: \(\dfrac{7}{9}-\dfrac{4}{9}=\dfrac{7-4}{9}=\dfrac{3}{9}=\dfrac{1}{3}\)
c: \(\dfrac{5}{6}+\dfrac{1}{8}=\dfrac{20}{24}+\dfrac{3}{24}=\dfrac{20+3}{24}=\dfrac{23}{24}\)
d: \(\dfrac{9}{15}-\dfrac{2}{5}=\dfrac{3}{5}-\dfrac{2}{5}=\dfrac{3-2}{5}=\dfrac{1}{5}\)
e: \(\dfrac{2}{5}+\dfrac{3}{5}+\dfrac{9}{5}=\dfrac{2+3+9}{5}=\dfrac{14}{5}\)
g: \(\dfrac{8}{10}-\dfrac{1}{10}-\dfrac{3}{10}=\dfrac{8-1-3}{10}=\dfrac{4}{10}=\dfrac{2}{5}\)
h: \(\dfrac{23}{7}-\dfrac{4}{7}+\dfrac{2}{7}=\dfrac{23-4+2}{7}=\dfrac{21}{7}=3\)
1 b) 
1 c) 
1 d) 
1
bài 1
a)\(=\dfrac{16}{40}+\dfrac{15}{40}=\dfrac{31}{40}\)
b)\(=\dfrac{7}{6}-\dfrac{4}{6}=\dfrac{3}{6}=\dfrac{1}{2}\)
c)\(=\dfrac{30}{9}=\dfrac{10}{3}\)
d)\(=\dfrac{8}{5}\times\dfrac{7}{4}=\dfrac{56}{20}=\dfrac{14}{5}\)
a: \(\dfrac{1}{8}+\dfrac{5}{8}=\dfrac{1+5}{8}=\dfrac{6}{8}=\dfrac{3}{4}\)
b: \(\dfrac{1}{15}+\dfrac{4}{15}=\dfrac{1+4}{15}=\dfrac{5}{15}=\dfrac{1}{3}\)
c: \(\dfrac{5}{9}+\dfrac{7}{9}=\dfrac{5+7}{9}=\dfrac{12}{9}=\dfrac{4}{3}\)
d: \(\dfrac{23}{100}+\dfrac{27}{100}=\dfrac{23+27}{100}=\dfrac{50}{100}=\dfrac{1}{2}\)
60x [7/12+4/15]
60x153/180
=9180/180
b 1/2x2/3x3/4x4/5x5/6x6/7x7/8x8/9=40320/4032
a) \(\dfrac{1}{2}-\dfrac{1}{6}=\dfrac{3}{6}-\dfrac{1}{6}=\dfrac{3-1}{6}=\dfrac{2}{6}=\dfrac{1}{3}\)
b) \(\dfrac{3}{4}-\dfrac{5}{8}=\dfrac{12}{8}-\dfrac{5}{8}=\dfrac{12-5}{8}=\dfrac{7}{8}\)
c) \(\dfrac{7}{10}-\dfrac{2}{5}=\dfrac{7}{10}-\dfrac{4}{10}=\dfrac{7-4}{10}=\dfrac{3}{10}\)
d) \(\dfrac{7}{12}-\dfrac{1}{3}=\dfrac{7}{12}-\dfrac{4}{12}=\dfrac{7-4}{12}=\dfrac{3}{12}=\dfrac{1}{4}\)
a: =6x5/4=30/4=15/2
b: =8x7/12=56/12=14/3
c: =5x8/7=40/7
d: =15x3/5=9
a: =6x5/4=30/4=15/2
b: =8x7/12=56/12=14/3
c: =5x8/7=40/7
d: =15x3/5=9