If cat and a half can catch mouse in day how many mice 3 cats days?

* One cat catches half a mouse in a day. (Since a cat and a half catches one mouse)

* One cat catches one mouse in two days. (Double the time for a single cat)

* Three cats catch three mice in two days. (Three times the cats, three times the mice)

* Three cats catch six mice in four days. (Double the time, double the mice)

Therefore, three cats can catch six mice in four days.