Bài 1:
\(\dfrac{36}{21}-\dfrac{15}{20}\)
\(=\dfrac{12}{7}-\dfrac{3}{4}\)
\(=\dfrac{48}{28}-\dfrac{21}{28}\)
\(=\dfrac{27}{28}\)
\(----\)
\(\dfrac{63}{45}-\dfrac{20}{25}\)
\(=\dfrac{63}{45}-\dfrac{4}{5}\)
\(=\dfrac{63}{45}-\dfrac{36}{45}\)
\(=\dfrac{27}{45}=\dfrac{3}{5}\)
Bài 2:
\(\dfrac{3}{5}+\dfrac{3}{16}+\dfrac{13}{16}\)
\(=\dfrac{3}{5}+\left(\dfrac{3}{16}+\dfrac{13}{16}\right)\)
\(=\dfrac{3}{5}+1\)
\(=\dfrac{3}{5}+\dfrac{5}{5}\)
\(=\dfrac{8}{5}\)
`36/21-15/20`
`=12/7-3/4`
`=48/28-21/28`
`=27/28`
__
`63/45-20/25`
`=7/5-4/5`
`=3/5`
__
`2)`
`3/5+3/16+13/16`
`=3/5+(3/16+13/16)`
`=3/5+16/16`
`=3/5+1`
`=3/5+5/5`
`=8/5`
`#QiN`
