expression to convert digital hours and minutes to a string

[phillip.howcroft]

I want to take a decimal which has been summed in by a variable to XXX.xx and convert it to YYY:yy where the yy is mins 

I can do this in SQL using

 TRUNC(Summary.Actual_Hrs) || ':' || SUBSTR (('00' || TRUNC(((Summary.Actual_Hrs) - TRUNC(Summary.Actual_Hrs))*60)), -2) AS Actual_Hrs

but i dont know how to do this in jaspersoft studio (5.6) using expressions. I've  trawled here and Google but it only gives references to time in dates not a summing of hours and minutes.  Can anyone point me in the right direction

Thanks