`3/5` $\text{và}$ `4/7`
`3/5 = {3xx7}/{5xx7} = 21/35`
`4/7 = {4xx5}/{7xx5} = 20/35`
_______________________
`2/3` $\text{và}$ `5/6`
`2/3 = {2xx6}/{3xx6} = 12/18`
`5/6 = {5xx3}/{3xx6} = 15/18`
___________________
`4/9` $\text{và}$ `1/6`
`4/9 = {4xx6}/{9xx6} = 24/54`
`1/6 = {1xx9}/{9xx6} = 9/54`