This short blog shows you why you cannot cast the division or int float DT_R8 using Derived Column.
I have a column ttMove is Integer and the value is 465. So, 465/60 should be 7.75.
I was putting the Expression (DT_R8)(ttMove / 60).
You need to remove the parenthesis () in order to get 7.75. So the right Expression should be (DT_R8)ttMove / 60 .