diff --git a/interfaces/demo2.go b/interfaces/demo2.go
new file mode 100644
index 0000000..3a59997
--- /dev/null
+++ b/interfaces/demo2.go
@@ -0,0 +1,54 @@
+package interfaces
+
+import "fmt"
+
+type Mortgage struct{
+	creditPaymentTotal float64
+	address string
+	rate float64
+}
+
+type Car struct{
+	creditPaymentTotal float64
+	carInfo string
+	rate float64
+}
+
+type CreditCalculator interface{
+	Calculate() float64
+}
+
+func (m Mortgage)  Calculate() float64{
+	return m.creditPaymentTotal * m.rate / 12
+}
+
+
+func (c Car)  Calculate() float64{
+	return c.creditPaymentTotal * c.rate / 12
+}
+
+func CalculateMonthlyPayment(credits []CreditCalculator)  float64{
+	
+	paymentTotal:= 0.0
+
+	for i := 0; i < len(credits); i++ {
+		paymentTotal = paymentTotal + (credits[i].Calculate())		
+	}
+	return paymentTotal
+}
+
+func Demo2()  {
+
+	credit1:= Mortgage{rate:10, creditPaymentTotal: 100000, address: "Ankara"}
+	
+	credit2:= Mortgage{rate:12, creditPaymentTotal: 50000, address: "İstanbul"}
+	
+	credit3:= Car{rate:15, creditPaymentTotal: 60000, carInfo:"Polo"}
+
+	credits:= []CreditCalculator{credit1, credit2, credit3}
+	
+	total:= CalculateMonthlyPayment(credits)
+
+	fmt.Println("Total payment", total)
+
+}
\ No newline at end of file
diff --git a/main.go b/main.go
index d3ab7a9..20d9132 100644
--- a/main.go
+++ b/main.go
@@ -78,4 +78,5 @@ func main() {
 	fmt.Println("Multiply Result : ", multiply)
 
 	interfaces.Demo1()
+	interfaces.Demo2()
 }