1 files changed, 16 insertions(+), 6 deletions(-)

M exercism/clojure/interest-is-interesting/src/interest_is_interesting.clj

@@ 1,16 1,26 @@
 (ns interest-is-interesting)
 
+(defn abs [x]
+  (max x (- x)))
+
 (defn interest-rate
-  "TODO: add docstring"
+  "Select interest rate depending on balance amount."
   [balance]
-  )
+  (cond (neg? balance) -3.213
+        (< balance 1000) 0.5
+        (< balance 5000) 1.621
+        :else 2.475))
 
 (defn annual-balance-update
-  "TODO: add docstring"
+  "Calculate new balance after interest rate yield."
   [balance]
-  )
+  (let [rate (/ (bigdec (interest-rate balance)) 100)
+        delta (* (abs balance) rate)]
+    (+ balance delta)))
 
 (defn amount-to-donate
-  "TODO: add docstring"
+  "Donate twice the allowed governmental tax-free donation amount."
   [balance tax-free-percentage]
-  )>
\ No newline at end of file
+  (let [tax-free-pct (/ tax-free-percentage 100)
+        tax-free-donation-amount (max 0 (* balance tax-free-pct))]
+    (int (* 2 tax-free-donation-amount))))