`4 . 5/7`
`=20/7`
__
`22/23 . 9/11`
`= 22.9/23.11`
`= 2.9/23.1`
`= 18/23`
__
`-9/7 . 7/15`
`= -9/15`
`= - 3/5`
\(a,4.\dfrac{5}{7}=\dfrac{4.5}{7}=\dfrac{20}{7}\)
\(b,\dfrac{22}{23}.\dfrac{9}{11}=\dfrac{22.9}{23.11}=\dfrac{198}{253}=\dfrac{18}{23}\)
\(c,\dfrac{-9}{7}.\dfrac{7}{15}=\dfrac{-9.7}{7.15}=\dfrac{-63}{105}=\dfrac{-3}{5}\)