[plt-scheme] best way to printf "%.2f" ?

Thanks for the quick reply!  I did try your suggestion.  It looks as though I have to add something to handle the tiny exponent (to get "6.67e-10"):

(require (lib "string.ss"))
...
> (running-time p2 2 2)
6.666666666666666e-10
> (real->decimal-string (running-time p2 2 2) 2)
"0.00"

-----Original Message-----
>From: Jens Axel Søgaard <jensaxel at soegaard.net>
>From (lib "string.ss"):
>
>(real->decimal-string n [digits-after-decimal-k])      PROCEDURE