diff --git a/dm5/lib/lib.ml b/dm5/lib/lib.ml
index cc347d6..2ffe31a 100644
--- a/dm5/lib/lib.ml
+++ b/dm5/lib/lib.ml
@@ -49,8 +49,8 @@ let bitonique t =
 
 (* Exercice 5 *)
 let psrn ta tb = Array.fold_left
-  (fun acc (a,b) -> acc + (a*b))
-  0
+  (fun acc (a,b) -> acc +. (a *. b))
+  0.
   (Array.map2
     (fun a b -> a,b)
     ta