`c)`
Ta có: `13/19 = 1 - 6/19`
và: `47/53 = 1 - 6/53`
Ta thấy: `19 < 53`
`⇒ 6/19 > 6/53`
`⇒ 1 - 6/19 < 1 - 6/53`
`⇒ 13/19 < 47/53`
Vậy `13/19 < 47/53`
`d)`
Ta có: `31/40` = `186/240`
Vì `240 < 241`
`⇒ 186/240 > 186/241`
`⇒ 31/40 > 186/241`
Vậy `31/40 > 186/241`