diff --git a/sicp-ex-1.11.rkt b/sicp-ex-1.11.rkt
new file mode 100644
index 0000000..2d858dd
--- /dev/null
+++ b/sicp-ex-1.11.rkt
@@ -0,0 +1,27 @@
+; f(n) = n, when n < 3
+; f(n) = f(n - 1) + f(n - 2) + f(n - 3), when n >= 3
+(define fn 15)
+
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+; recursive
+(define (f-rec n)
+  (if (< n 3)
+      n
+      (+ (+ (f-rec (- n 1))
+            (f-rec (- n 2)))
+         (f-rec (- n 3)))))
+
+(f-rec fn)
+
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+; iterative
+(define (f-iter n)
+  (f-iter-step 2 1 0 n))
+
+(define (f-iter-step a b c count)
+  (if (< count 3)
+      a
+      (f-iter-step (+ a b c) a b (- count 1))))
+
+(f-iter fn)
+