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C1 : 3/4 x 1/2 x 2
= 3/8 x 2
= 3/4
C2 : 3/4 x 1/2 x 2
= 3/4 x ( 1/2 x 2 )
= 3/4 x 1
= 3/4
72 x 135 + 9 x 28 x 15 = 13500
13500 : 25 = 540
3500 : 25 = 140
540 - 140 = 400
a) \(\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}\)
\(=1-\frac{1}{4}\)
\(=\frac{3}{4}\)
b) \(\frac{4}{7}\times\frac{8}{9}+\frac{4}{7}\times\frac{1}{9}\)
\(=\frac{4}{7}\times\left(\frac{8}{9}+\frac{1}{9}\right)\)
\(=\frac{4}{7}\times1\)
\(=\frac{4}{7}\)
c) \(\frac{13}{6}\times\frac{3}{8}-\frac{3}{8}\times\frac{7}{6}\)
\(=\frac{3}{8}\times\left(\frac{13}{6}-\frac{7}{6}\right)\)
\(=\frac{3}{8}\times1\)
\(=\frac{3}{8}\)
d) \(\frac{1}{1x2}+\frac{1}{2x3}+\frac{1}{3x4}+...+\frac{1}{9x10}\)
\(=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{9}-\frac{1}{10}\)
\(=1-\frac{1}{10}\)
\(=\frac{9}{10}\)
3/2 nha bn
\(\frac{3}{2}\times\frac{4}{7}+\frac{3}{7}\times\frac{3}{2}\)
\(=\frac{3}{2}\times\left(\frac{4}{7}+\frac{3}{7}\right)\)
\(=\frac{3}{2}\times1\)
\(=\frac{3}{2}\)
#H