diff --git a/01-hello.rb b/01-hello.rb
index e0e7bbf..2a27733 100644
--- a/01-hello.rb
+++ b/01-hello.rb
@@ -1,8 +1,5 @@
 # 题目: 输入名字，输出 "Hello, 名字"
 
 print "请输入你的名字，然后按 Enter: "
-your_name = gets
-
-# ...
-
-puts "(请替换成最后的答案)"
\ No newline at end of file
+your_name = gets   # 从键盘拿到输入的值
+puts "Hello, #{your_name}"   # 输出值，并且有换行
diff --git a/02-variable.rb b/02-variable.rb
index a5a4753..53b4c95 100644
--- a/02-variable.rb
+++ b/02-variable.rb
@@ -6,8 +6,9 @@
 puts "a 是 #{a}"
 puts "b 是 #{b}"
 
-# ...
+c = a
+a = b
+b = c
 
 puts "a 应该是 2，现在是 #{a}"
 puts "b 应该是 1，现在是 #{b}"
-
diff --git a/03-triangle.rb b/03-triangle.rb
index fafec03..806b962 100644
--- a/03-triangle.rb
+++ b/03-triangle.rb
@@ -2,10 +2,12 @@
 
 print "请输入直角三角形的高，然后按 Enter: "
 a = gets
+a = a.to_f
 
 print "请输入直角三角形的底边，然后按 Enter: "
 b = gets
+b = b.to_f
 
-# .....
+area = a * b / 2
 
-puts "直角三角形的面积是: _________"
\ No newline at end of file
+puts "直角三角形的面积是: #{area}"
diff --git a/04-pizzas.rb b/04-pizzas.rb
index 4c2521f..77cd48c 100644
--- a/04-pizzas.rb
+++ b/04-pizzas.rb
@@ -2,11 +2,14 @@
 
 print "请输入有多少片比萨饼，然后按 Enter: "
 pizzas = gets
+pizzas = pizzas.to_i
 
 print "请输入有多少人要吃，然后按 Enter: "
 people = gets
+people = people.to_i
 
-# .....
+per = pizzas / people
+remain = pizzas % people
 
-puts "每人可分得几片: _________ 片"
-puts "还剩下几片: _________ 片"
\ No newline at end of file
+puts "每人可分得 #{per} 片"
+puts "还剩下 #{remain} 片"
diff --git a/05-bmi.rb b/05-bmi.rb
index 67efdff..9a50a95 100644
--- a/05-bmi.rb
+++ b/05-bmi.rb
@@ -6,12 +6,22 @@
 
 print "请输入您的体重(公斤)，然后按 Enter: "
 weight = gets
+weight = weight.to_f
 
 print "请输入您的身高(厘米)，然后按 Enter: "
 height = gets
+height = height.to_f
 
-# .....
+bmi = weight / (height * height)
 
-puts "您的 BMI 是: _________"
+if bmi < 18.5
+  result = "过轻"
+elsif bmi >= 24
+  result = "过重"
+else
+  result = "正常"
+end
 
-puts "您的 BMI 结果是: _________(过轻或正常或过重)"
\ No newline at end of file
+puts "您的 BMI 是: #{bmi} "
+
+puts "您的 BMI 结果是: #{result}"
diff --git a/06-interger-positive.rb b/06-interger-positive.rb
index a240f5f..fd8aed5 100644
--- a/06-interger-positive.rb
+++ b/06-interger-positive.rb
@@ -3,8 +3,21 @@
 
 print "请输入一个整数，然后按 Enter: "
 x = gets
+x = x.to_i
 
-# ....
+if x > 0
+  result1 = "正数"
+elsif x < 0
+  result1 = "负数"
+else
+  result1 = "零"
+end
 
-puts "这个数是_____ (正数或零或负数)"
-puts "这个数是_____ (偶数或奇数)"
\ No newline at end of file
+if x % 2 == 0
+  result2 = "偶数"
+else
+  result2 = "奇数"
+end
+
+puts "这个数是 #{result1}"
+puts "这个数是 #{result2}"
diff --git a/07-abcde.rb b/07-abcde.rb
index 5d0c8c3..891d0fa 100644
--- a/07-abcde.rb
+++ b/07-abcde.rb
@@ -10,13 +10,32 @@
 
 print "请输入一个整数x，然后按 Enter: "
 x = gets
+x = x.to_i
 
 print "请输入一个整数y，然后按 Enter: "
 y = gets
+y = y.to_i
 
 print "请输入一个整数z，然后按 Enter: "
 z = gets
+z = z.to_i
 
-# ....
+if x < 0
+  result = "A"
+elsif x > 0
+  if y > 0
+    if z > 0
+      result = "B"
+    elsif z < 0
+      result = "C"
+    end
+  elsif y < 0
+    if z > 0
+      result = "D"
+    elsif z < 0
+      result = "E"
+    end
+  end
+end
 
-puts "结果是________(A或B或C或D或E)"
\ No newline at end of file
+puts "结果是 #{result}"
diff --git a/08-find-max.rb b/08-find-max.rb
index 9e6e643..3104308 100644
--- a/08-find-max.rb
+++ b/08-find-max.rb
@@ -2,13 +2,16 @@
 
 print "请输入一个数字x，然后按 Enter: "
 x = gets
+x = x.to_f
 
 print "请输入一个数字y，然后按 Enter: "
 y = gets
+y = y.to_f
 
 print "请输入一个数字z，然后按 Enter: "
 z = gets
+z = z.to_f
 
-# ....
+max = [x, y, z].max
 
-puts "最大的数是 ________(x或y或z)"
\ No newline at end of file
+puts "最大的数是 #{max}"
diff --git a/09-function.rb b/09-function.rb
index b1f922d..3591a7f 100644
--- a/09-function.rb
+++ b/09-function.rb
@@ -1,15 +1,17 @@
 # 题目: 输入直角三角形的宽和高，输出三角形的面积
 
 def calculate_area(a, b)
-  # ....
+  a * b
 end
 
 print "请输入直角三角形的高，然后按 Enter: "
 a = gets
+a = a.to_f
 
 print "请输入直角三角形的底边，然后按 Enter: "
 b = gets
+b = b.to_f
 
 answer = calculate_area(a,b)
 
-puts "直角三角形的面积是: #{answer}"
\ No newline at end of file
+puts "直角三角形的面积是: #{answer}"
diff --git a/10-function.rb b/10-function.rb
index bb450fb..b4a2f73 100644
--- a/10-function.rb
+++ b/10-function.rb
@@ -1,19 +1,21 @@
 # 题目: 使用者输入 x,y,z，请输出三个数中最大的数
 
 def find_max(x, y, z)
+  [x, y, z].max
 end
 
 print "请输入一个数字x，然后按 Enter: "
 x = gets
+x = x.to_f
 
 print "请输入一个数字y，然后按 Enter: "
 y = gets
+y = y.to_f
 
 print "请输入一个数字z，然后按 Enter: "
 z = gets
-
-# ....
+z = z.to_f
 
 answer = find_max(x,y,z)
 
-puts "最大的数是 #{answer}"
\ No newline at end of file
+puts "最大的数是 #{answer}"
diff --git a/11-seven.rb b/11-seven.rb
index 26c221d..5b01f64 100644
--- a/11-seven.rb
+++ b/11-seven.rb
@@ -2,8 +2,8 @@
 
 i = 1
 while ( i <= 100 )
-
-  # ....
-
+  if i % 7 == 0
+    puts i
+  end
   i+=1
-end
\ No newline at end of file
+end
diff --git a/12-sum-even.rb b/12-sum-even.rb
index 73879bb..cb6aa4f 100644
--- a/12-sum-even.rb
+++ b/12-sum-even.rb
@@ -4,10 +4,10 @@
 total = 0
 
 while ( i <= 100 )
-
-  # ....
-
+  if i % 2 == 0
+    total = total + i
+  end
   i+=1
 end
 
-puts total
\ No newline at end of file
+puts total
diff --git a/13-nn.rb b/13-nn.rb
index ac0a43b..5458e3c 100644
--- a/13-nn.rb
+++ b/13-nn.rb
@@ -2,10 +2,14 @@
 
 print "请输入数字 N，然后按 Enter: "
 n = gets
+n = n.to_i
 
-# while ( ... )
-#   while ( ...)
-#
-#   end
-# end
-
+x = 0
+while x <= n
+  y = 0
+  while y <= n
+    puts "#{x} x #{y} = #{x * y}"
+    y+=1
+  end
+  x+=1
+end
diff --git a/14-prime.rb b/14-prime.rb
index 8cf1692..78e413b 100644
--- a/14-prime.rb
+++ b/14-prime.rb
@@ -1,9 +1,27 @@
 # 输入一个数字 N，请检查是不是质数
 
 def is_prime(n)
-# ....
+  if n < 2
+    return false
+  end
+
+  if n == 2
+    return true
+  end
+
+  if n > 2
+    i = 2
+    while i <= n / 2
+      if n % i == 0
+        return false
+      end
+      i+=1
+    end
+    return true
+  end
 end
 
+
 print "请输入数字 N，然后按 Enter: "
 n = gets
 
diff --git a/15-guess-number.rb b/15-guess-number.rb
index 48f9dca..f9e5456 100644
--- a/15-guess-number.rb
+++ b/15-guess-number.rb
@@ -6,12 +6,17 @@
   print "请猜一个 0~99 的数字 N，然后按 Enter: "
   n = gets
 
-  #puts "太低了，再猜一次"
-  #puts "太高了，再猜一次"
+  if n.to_i < target
+    puts "太低了，再猜一次"
+  end
+
+  if n.to_i > target
+    puts "太高了，再猜一次"
+  end
 
   if n.to_i == target
     puts "恭喜猜中啦! "
     break
   end
 
-end
\ No newline at end of file
+end
diff --git a/16-array-sum.rb b/16-array-sum.rb
index 9b4910b..983e7b6 100644
--- a/16-array-sum.rb
+++ b/16-array-sum.rb
@@ -1,11 +1,10 @@
 # 给定一阵列内含数字，输出最大值
 
 def find_max(array)
-  #....
+  array.max
 end
 
-arr = [8, 12, 36, 53, 9, 75, 3, 71, 59, 88]
+arr = [8, 12, 36, 53, 9, 75, 3, 71, 59, 88, 102]
 
 max = find_max(arr)
-puts "Max is #{max}" # 应该是 88
-
+puts "Max is #{max}" 
diff --git a/17-array-stats.rb b/17-array-stats.rb
index 0af81bb..0f77155 100644
--- a/17-array-stats.rb
+++ b/17-array-stats.rb
@@ -12,9 +12,14 @@
   end
 end
 
+sum = 0
+arr.each do |i|
+  sum = sum + i
+end
+
 puts arr.to_s
 
-puts "总和是 _____"
-puts "平均是 _____"
-puts "最大值是 _____"
-puts "最小值是 _____"
\ No newline at end of file
+puts "总和是 #{sum}"
+puts "平均是 #{sum / arr.length}"
+puts "最大值是 #{arr.max}"
+puts "最小值是 #{arr.min}"
diff --git a/18-square.rb b/18-square.rb
index 226e1c1..6b2595f 100644
--- a/18-square.rb
+++ b/18-square.rb
@@ -1,10 +1,12 @@
-# 建构一个阵列有一百个的元素，内容是 0, 1, 4, 9, 16, 25...... 每个元素是该索引的平方
+# 建构一个阵列有N的元素，内容是 0, 1, 4, 9, 16, 25...... 每个元素是该索引的平方
 
 arr = []
 
 print "请输入数字 N，然后按 Enter: "
-n = gets
+n = gets().to_i
 
-# ...
+(0..n-1).each_with_index do |i|
+  arr << i ** 2
+end
 
-puts arr.to_s
\ No newline at end of file
+puts arr.to_s
diff --git a/19-filter.rb b/19-filter.rb
index ef7e515..0e397ed 100644
--- a/19-filter.rb
+++ b/19-filter.rb
@@ -1,9 +1,15 @@
 # 给定一阵列内含数字，输出另一个数组只包含偶数
 
 def filter_even(arr)
-  #...
+  filter_even = []
+  arr.each do |i|
+    if i % 2 == 0
+      filter_even << i
+    end
+  end
+  filter_even
 end
 
 arr =  [7, 68, 42, 46, 9, 91, 77, 46, 86, 1]
 
-puts filter_even(arr).to_s # 应该是 [68, 42, 46, 46, 86]
\ No newline at end of file
+puts filter_even(arr).to_s # 应该是 [68, 42, 46, 46, 86]
diff --git a/20-sorting.rb b/20-sorting.rb
index 5f82c08..71c5d4a 100644
--- a/20-sorting.rb
+++ b/20-sorting.rb
@@ -2,10 +2,15 @@
 # Hint: 可用 arr.sort 排序，和 arr.uniq 去除重复
 
 def filter_even(arr)
-  #...
+  filter_even = []
+  arr.each do |i|
+    if i % 2 == 0
+      filter_even << i
+    end
+  end
+  filter_even
 end
 
 arr =  [7, 68, 42, 46, 9, 91, 77, 46, 86, 1]
 
-
-puts "________" # 应该是 [42, 46, 68, 86]
\ No newline at end of file
+puts filter_even(arr).sort.uniq.to_s   # 应该是 [42, 46, 68, 86]
diff --git a/21-selection-sort.rb b/21-selection-sort.rb
index e5e7eae..8eea8bf 100644
--- a/21-selection-sort.rb
+++ b/21-selection-sort.rb
@@ -2,11 +2,17 @@
 # https://zh.wikipedia.org/wiki/选择排序
 
 def selection_sort(arr)
-  #...
+  (0...arr.length).each do |i|
+    min, index = arr[i], i
+    (i...arr.length).each { |j| min, index = arr[j], j if arr[j] < min }
+    arr[i], arr[index] = arr[index], arr[i]
+  end
+arr
+
 end
 
 arr =  [7, 68, 42, 46, 9, 91, 77, 46, 86, 1]
 
 answer = selection_sort(arr)
 
-puts answer.to_s # 应该是 [1, 7, 9, 42, 46, 46, 68, 77, 86, 91]
\ No newline at end of file
+puts answer.to_s # 应该是 [1, 7, 9, 42, 46, 46, 68, 77, 86, 91]
diff --git a/22-missing.rb b/22-missing.rb
index 6898714..06cba38 100644
--- a/22-missing.rb
+++ b/22-missing.rb
@@ -1,7 +1,11 @@
 # 给定一阵列内含数字，请输出 0~9 中不见的数字
 
 def find_missing(arr)
-  # ...
+  missing_number = []
+  (0..9).each do |i|
+    missing_number << i unless arr.include?(i)
+  end
+  missing_number
 end
 
 answer = find_missing( [2,2,1,5,8,4] )
diff --git a/23-hash-max.rb b/23-hash-max.rb
index 6fb227e..0978898 100644
--- a/23-hash-max.rb
+++ b/23-hash-max.rb
@@ -1,19 +1,19 @@
 # 给定一 Hash，输出有最大 value 的 key
 
 def find_max(hash)
-  # ...
+  hash.each do |key, value|
+    return key if value == hash.values.max
+  end
 end
 
 h = {
   "a" => 71,
   "b" => 38,
-  "c" => 21,
+  "c" => 121,
   "d" => 80,
   "e" => 10
 }
 
 answer = find_max(h)
 
-puts "有最大 value 的是 #{answer}" # 应该是 d
-
-
+puts "有最大 value 的是 #{answer}" 
diff --git a/24-hash-even.rb b/24-hash-even.rb
index 9da9605..efb04df 100644
--- a/24-hash-even.rb
+++ b/24-hash-even.rb
@@ -1,9 +1,11 @@
 # 给定一 Hash，输出 value 是偶数的 keys
 
 def find_even_keys(hash)
-
-  # ... (请回传一个数组)
-
+  answer = []
+  hash.each do |key, value|
+    answer << key if value % 2 == 0
+  end
+  answer
 end
 
 h = {
@@ -17,5 +19,3 @@ def find_even_keys(hash)
 answer = find_even_keys(h)
 
 puts "有偶数 value 的 keys 有 #{answer}" # 应该是数组 [b,d,e]
-
-
diff --git a/25-hash-count.rb b/25-hash-count.rb
index 2167335..2b4e6bc 100644
--- a/25-hash-count.rb
+++ b/25-hash-count.rb
@@ -4,7 +4,8 @@ def count(arr)
   h = {}
 
   arr.each do |i|
-    # ...
+    a = arr.count(i)
+    h[i] = a
   end
 
   return h # 回传一个 hash
@@ -15,4 +16,3 @@ def count(arr)
 answer = count(arr)
 
 puts answer # 答案应该是 {"a"=>3, "d"=>6, "c"=>5, "b"=>1, "e"=>5}
-
diff --git a/26-hash-filter.rb b/26-hash-filter.rb
index 51ade64..27699c7 100644
--- a/26-hash-filter.rb
+++ b/26-hash-filter.rb
@@ -8,9 +8,18 @@
   { "name" => "Vincent", "age" => 6 },
 ]
 
-# ....
+def filter(arr)
+  result = []
+  arr.each do |h|
+      if h["age"] >= 18
+        result << h
+      end
+  end
 
-puts "所有成年人，并由小到大: _________"
+  result.sort_by { |i| i["age"] }
+end
+
+puts "所有成年人，并由小到大: #{filter(arr)}"
 
 # 答案应该是
 #[
diff --git a/27-class.rb b/27-class.rb
index 8cec2c9..965dc58 100644
--- a/27-class.rb
+++ b/27-class.rb
@@ -1,5 +1,9 @@
 class Person
-  # ...
+  attr_accessor :first_name, :last_name
+  
+  def greet
+    puts "Hello, #{first_name} #{last_name}"
+  end
 end
 
 p1 = Person.new
@@ -11,6 +15,3 @@ class Person
 p2.first_name = "William"
 p2.last_name = "Zhang"
 p2.greet # 输出 "Hello, William Zhang"
-
-
-
diff --git a/28-word-count.rb b/28-word-count.rb
index 2643123..9af0119 100644
--- a/28-word-count.rb
+++ b/28-word-count.rb
@@ -2,4 +2,12 @@
 
 doc = File.read("wordcount.txt")
 
-# ...
+words = doc.downcase.scan(/\w+/)
+
+result = {}
+
+words.each do |i|
+  result[i] = words.count(i)
+end
+
+puts result
diff --git a/29-todos.rb b/29-todos.rb
index 0bddde2..ec5f78b 100644
--- a/29-todos.rb
+++ b/29-todos.rb
@@ -1,5 +1,7 @@
 # 简易 Todo 代办事项应用
 
+require 'byebug'
+
 text = File.read("todos.txt")
 
 todos = []
@@ -17,17 +19,26 @@
 
   if command == "add"
     print "请输入代办事项: "
-    # ...
+    todos << gets
   elsif command == "remove"
     print "请输入要删除的编号: "
-    # ...
+    choose = gets().to_i
+    todos.delete_at(choose)
   elsif command == "save"
     puts "存盘离开"
 
-    # ...
+    File.open("todos.txt", "w+") do |f|
+      for a in todos
+        f << a + "\n"
+      end
+    end
+
+    todos.each_with_index do |todo, index|
+      puts "#{index}: #{todo}"
+    end
+
     break;
   else
     puts "看不懂，请再输入一次"
   end
 end
-
diff --git a/todos.txt b/todos.txt
index 4757e85..f7988fa 100644
--- a/todos.txt
+++ b/todos.txt
@@ -1,4 +1,5 @@
 Buy book
 Go Shopping
 Walk
-Gogo
+Have dinner
+