diff --git a/src/main/scala/practise4/demo/Demo.scala b/src/main/scala/practise4/demo/Demo.scala
new file mode 100644
index 0000000..0823341
--- /dev/null
+++ b/src/main/scala/practise4/demo/Demo.scala
@@ -0,0 +1,16 @@
+package practise4.demo
+
+object Demo {
+  def main(args: Array[String]): Unit = {
+    // 现在我们解决你前面最容易产生疑问的地方：
+
+    def add(a: Int, b: Int): Int = a + b
+
+    val add2 = (a: Int, b: Int) => a + b
+
+    // 为什么都能：
+
+    println(add(10, 20))
+    println(add2(10, 20))
+  }
+}
diff --git a/src/main/scala/practise4/exercises/Exercises1.scala b/src/main/scala/practise4/exercises/Exercises1.scala
new file mode 100644
index 0000000..008a8be
--- /dev/null
+++ b/src/main/scala/practise4/exercises/Exercises1.scala
@@ -0,0 +1,20 @@
+package practise4.exercises
+
+/*
+  练习1
+
+  写一个：
+  val triple = ...
+
+  要求：
+  println(triple(5))
+
+  输出：
+  15
+  */
+object Exercises1 {
+  def main(args: Array[String]): Unit = {
+    val triple = (x: Int) => x * 3
+    println(triple(5))
+  }
+}
diff --git a/src/main/scala/practise4/exercises/Exercises2.scala b/src/main/scala/practise4/exercises/Exercises2.scala
new file mode 100644
index 0000000..908fd96
--- /dev/null
+++ b/src/main/scala/practise4/exercises/Exercises2.scala
@@ -0,0 +1,20 @@
+package practise4.exercises
+
+/*
+练习 2
+
+给：
+val nums = List(1, 2, 3, 4, 5)
+
+使用 map：
+每个元素乘 10
+
+结果：
+List(10, 20, 30, 40, 50)*/
+object Exercises2 {
+  def main(args: Array[String]): Unit = {
+    val nums = List(1, 2, 3, 4, 5)
+    val result = nums.map(x => x * 10)
+    println(result)
+  }
+}
diff --git a/src/main/scala/practise4/exercises/Exercises3.scala b/src/main/scala/practise4/exercises/Exercises3.scala
new file mode 100644
index 0000000..1cd9247
--- /dev/null
+++ b/src/main/scala/practise4/exercises/Exercises3.scala
@@ -0,0 +1,19 @@
+package practise4.exercises
+
+/*
+练习 3
+
+给：
+val nums = List(10, 15, 20, 25, 30)
+
+使用 filter：
+只保留 >= 20 的数字
+*/
+
+object Exercises3 {
+  def main(args: Array[String]): Unit = {
+    val nums = List(10, 15, 20, 25, 30)
+    val result = nums.filter(x => x >= 20)
+    println(result)
+  }
+}
diff --git a/src/main/scala/practise4/exercises/Exercises4.scala b/src/main/scala/practise4/exercises/Exercises4.scala
new file mode 100644
index 0000000..3ab806b
--- /dev/null
+++ b/src/main/scala/practise4/exercises/Exercises4.scala
@@ -0,0 +1,29 @@
+package practise4.exercises
+/*
+练习 4
+
+给：
+val nums = List(1, 2, 3, 4, 5)
+
+要求：
+先乘 2
+再只保留 >= 6
+
+最终：
+List(6, 8, 10)
+
+提示，你可以继续使用链式调用：
+nums
+  .map(...)
+.filter(...)
+*/
+
+object Exercises4 {
+  def main(args: Array[String]): Unit = {
+    val nums = List(1, 2, 3, 4, 5)
+    val result = nums
+      .map(x => x * 2)
+      .filter(x => x >= 6)
+    println(result)
+  }
+}
diff --git a/src/main/scala/practise4/exercises/Exercises5.scala b/src/main/scala/practise4/exercises/Exercises5.scala
new file mode 100644
index 0000000..cede719
--- /dev/null
+++ b/src/main/scala/practise4/exercises/Exercises5.scala
@@ -0,0 +1,29 @@
+package practise4.exercises
+
+/*
+练习 5 ⭐
+这次不用 map。
+
+写一个函数：
+val calc = ...
+
+要求：
+println(calc(10, 20))
+
+输出：
+30
+
+然后再创建：
+val result = calc(5, 8)
+
+要求 result 是：
+13
+*/
+object Exercises5 {
+  def main(args: Array[String]): Unit = {
+    val calc = (a: Int, b: Int) => a + b
+    println(calc(10, 20))
+    val result = calc(5, 8)
+    println(result)
+  }
+}