`a)64/85` và `73/81`
`64/85<64/81`
`73/81>64/81`
Vậy `64/85<73/81`
`b)456/461` và `123/128`
`456/461=461/461-5/461=1-5/461`
`123/128=128/128-5/128=1-5/128`
Mà `5/128>5/461`
Vậy `456/461<123/128`
`c)58/89` và `36/63`
`36/63=4/7=356/623`
`58/89=406/623`
Mà `406/623>356/623`
Vậy `58/89>36/63`
`d)213/207` và `519/513`
`213/207=207/207+6/207=1+6/207`
`519/513=513/513+6/513=1+6/513`
Mà `6/207>6/513`
Vậy `213/207>519/513.`