newbie question: print rational as decimal number



what am I supposed to do for printing

r : 254471799841260872232137838180485/566407006423962932969881084235776;

as decimal number?

printf( true, "~f~%", r );

does not work

r : 2/3;

should result in

1.5


Best regards

Andre

P.S.: the Maple equivalent would be feval