Answer:
Common denominator 20
![(3)/( \: 4 \:) \: and \: (2)/(5)](https://img.qammunity.org/2021/formulas/mathematics/middle-school/u8a2aec4klqsg93o189xb2ekbxgaz45of1.png)
because 4 and 5 can both go into 20 without any remainder
Common denominator 18
![(3)/(6) and \: (2)/(9)](https://img.qammunity.org/2021/formulas/mathematics/middle-school/jjik2oloe7s653af0zqal90mm0zwni3uj7.png)
because 6 and 9 can both go into 18 without any remainder
Common denominator 8
![(1)/(2) \: and \: (7)/(8)](https://img.qammunity.org/2021/formulas/mathematics/middle-school/mo7atpy8f47b0dvocrzw5g5abgcaxjaqbn.png)
because 2 and 8 can both go into 8 without any remainder
Hope this was helpful!