diff --git a/01-hello.rb b/01-hello.rb
index e0e7bbf..586a8f1 100644
--- a/01-hello.rb
+++ b/01-hello.rb
@@ -5,4 +5,4 @@
 
 # ...
 
-puts "(请替换成最后的答案)"
\ No newline at end of file
+puts "hello, " + your_name
diff --git a/02-variable.rb b/02-variable.rb
index a5a4753..2821710 100644
--- a/02-variable.rb
+++ b/02-variable.rb
@@ -8,6 +8,5 @@
 
 # ...
 
-puts "a 应该是 2，现在是 #{a}"
-puts "b 应该是 1，现在是 #{b}"
-
+puts "a 应该是 2，现在是 #{b}"
+puts "b 应该是 1，现在是 #{a}"
diff --git a/03-triangle.rb b/03-triangle.rb
index fafec03..e136a56 100644
--- a/03-triangle.rb
+++ b/03-triangle.rb
@@ -8,4 +8,4 @@
 
 # .....
 
-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: #{ a.to_f*b.to_f/2 }"
diff --git a/04-pizzas.rb b/04-pizzas.rb
index 4c2521f..09c95a5 100644
--- a/04-pizzas.rb
+++ b/04-pizzas.rb
@@ -1,12 +1,12 @@
 # 题目: 输入有多少片比萨饼和多少人，输出每人可以分到几片，以及剩下几片
 
 print "请输入有多少片比萨饼，然后按 Enter: "
-pizzas = gets
+pizzas = gets.to_i
 
 print "请输入有多少人要吃，然后按 Enter: "
-people = gets
+people = gets.to_i
 
 # .....
 
-puts "每人可分得几片: _________ 片"
-puts "还剩下几片: _________ 片"
\ No newline at end of file
+puts "每人可分得几片: #{(pizzas / people).ceil} 片"
+puts "还剩下几片: #{ pizzas % people } 片"
diff --git a/05-bmi.rb b/05-bmi.rb
index 67efdff..94424e4 100644
--- a/05-bmi.rb
+++ b/05-bmi.rb
@@ -5,13 +5,25 @@
 # 如果 BMI 介于 18.5 ~ 24，显示正常
 
 print "请输入您的体重(公斤)，然后按 Enter: "
-weight = gets
+weight = gets.to_f
 
 print "请输入您的身高(厘米)，然后按 Enter: "
-height = gets
+height = gets.to_f / 100
 
 # .....
 
-puts "您的 BMI 是: _________"
+bmi = (weight / (height * height))
+bmis = bmi.to_s
+bmi_rounddown = bmis[0, bmis.index('.')+2+1].to_f
 
-puts "您的 BMI 结果是: _________(过轻或正常或过重)"
\ No newline at end of file
+if bmi < 18.5
+  result = "过轻"
+elsif bmi >= 24
+  result = "过重"
+else
+  result = "正常"
+end
+
+puts "您的 BMI 是: #{bmi_rounddown}"
+
+puts "您的 BMI 结果是: #{result}"
diff --git a/06-interger-positive.rb b/06-interger-positive.rb
index a240f5f..4f89d48 100644
--- a/06-interger-positive.rb
+++ b/06-interger-positive.rb
@@ -2,9 +2,16 @@
 
 
 print "请输入一个整数，然后按 Enter: "
-x = gets
+x = gets.to_i
 
-# ....
+result = "零"
+if x > 0
+  result = "正数"
+elsif x < 0
+  result = "负数"
+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
+odd = (x % 2 == 0 ? "偶数" : "奇数")
+
+puts "这个数是 #{result} (正数或零或负数)"
+puts "这个数是 #{odd} (偶数或奇数)"
diff --git a/07-abcde.rb b/07-abcde.rb
index 5d0c8c3..7553f0d 100644
--- a/07-abcde.rb
+++ b/07-abcde.rb
@@ -9,14 +9,30 @@
 #     当 z < 0 输出 "E"
 
 print "请输入一个整数x，然后按 Enter: "
-x = gets
+x = gets.to_i
 
 print "请输入一个整数y，然后按 Enter: "
-y = gets
+y = gets.to_i
 
 print "请输入一个整数z，然后按 Enter: "
-z = gets
+z = gets.to_i
 
 # ....
 
-puts "结果是________(A或B或C或D或E)"
\ No newline at end of file
+if x < 0
+  result = "A"
+elsif 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
+
+puts "结果是#{result}"
diff --git a/08-find-max.rb b/08-find-max.rb
index 9e6e643..ed117af 100644
--- a/08-find-max.rb
+++ b/08-find-max.rb
@@ -1,14 +1,17 @@
 # 题目: 使用者输入 x,y,z，请输出三个数中最大的数
 
 print "请输入一个数字x，然后按 Enter: "
-x = gets
+x = gets.to_i
 
 print "请输入一个数字y，然后按 Enter: "
-y = gets
+y = gets.to_i
 
 print "请输入一个数字z，然后按 Enter: "
-z = gets
+z = gets.to_i
 
 # ....
 
-puts "最大的数是 ________(x或y或z)"
\ No newline at end of file
+result = x > y ? x : y
+result = result > z ? result : z
+
+puts "最大的数是 #{result}"
diff --git a/09-function.rb b/09-function.rb
index b1f922d..70aa9e9 100644
--- a/09-function.rb
+++ b/09-function.rb
@@ -1,15 +1,15 @@
 # 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 / 2
 end
 
 print "请输入直角三角形的高，然后按 Enter: "
-a = gets
+a = gets.to_f
 
 print "请输入直角三角形的底边，然后按 Enter: "
-b = gets
+b = gets.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..f1a04e5 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)
+  result = x > y ? x : y
+  return result > z ? result : z
 end
 
 print "请输入一个数字x，然后按 Enter: "
-x = gets
+x = gets.to_f
 
 print "请输入一个数字y，然后按 Enter: "
-y = gets
+y = gets.to_f
 
 print "请输入一个数字z，然后按 Enter: "
-z = gets
+z = gets.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..747cef3 100644
--- a/11-seven.rb
+++ b/11-seven.rb
@@ -1,9 +1,8 @@
 # 题目: 列出 1 到 100 之间，所有 7 的倍数
 
 i = 1
-while ( i <= 100 )
+while i <= 100
 
-  # ....
-
-  i+=1
-end
\ No newline at end of file
+  puts i if i % 7 == 0
+  i += 1
+end
diff --git a/12-sum-even.rb b/12-sum-even.rb
index 73879bb..042b03a 100644
--- a/12-sum-even.rb
+++ b/12-sum-even.rb
@@ -5,9 +5,10 @@
 
 while ( i <= 100 )
 
-  # ....
-
+  if (i % 2 == 0)
+    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..3ca3d00 100644
--- a/13-nn.rb
+++ b/13-nn.rb
@@ -1,11 +1,13 @@
 # 题目: 输入一个数字 N，输出 N * N 乘法表
 
 print "请输入数字 N，然后按 Enter: "
-n = gets
-
-# while ( ... )
-#   while ( ...)
-#
-#   end
-# end
-
+n = gets.to_i
+i = 0
+while  i <= n
+  j = 0
+  while  j <= n
+    puts "#{i} × #{j} = #{i*j}"
+    j = j + 1
+  end
+  i = i + 1
+end
diff --git a/14-prime.rb b/14-prime.rb
index 8cf1692..a65ce29 100644
--- a/14-prime.rb
+++ b/14-prime.rb
@@ -1,7 +1,14 @@
 # 输入一个数字 N，请检查是不是质数
 
 def is_prime(n)
-# ....
+  i = 2
+  while i < (n/2).to_i
+    if n % i == 0
+      return false
+    end
+    i = i + 1
+  end
+  return true
 end
 
 print "请输入数字 N，然后按 Enter: "
diff --git a/15-guess-number.rb b/15-guess-number.rb
index 48f9dca..5b81912 100644
--- a/15-guess-number.rb
+++ b/15-guess-number.rb
@@ -2,16 +2,17 @@
 
 target = rand(100)
 
-while (true)
-  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"
+loop do
+  print '请猜一个 0~99 的数字 N，然后按 Enter: '
+  n = gets.to_i
+  if n > target
+    puts '太高了，再猜一次'
+  elsif n < target
+    puts '太低了，再猜一次'
+  end
 
   if n.to_i == target
-    puts "恭喜猜中啦! "
+    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..b48e1e7 100644
--- a/16-array-sum.rb
+++ b/16-array-sum.rb
@@ -1,7 +1,12 @@
 # 给定一阵列内含数字，输出最大值
 
-def find_max(array)
-  #....
+def find_max(_array)
+  # _array.max
+  max = 0
+  _array.each do |i|
+    max = i if max < i
+  end
+  max
 end
 
 arr = [8, 12, 36, 53, 9, 75, 3, 71, 59, 88]
@@ -9,3 +14,7 @@ def find_max(array)
 max = find_max(arr)
 puts "Max is #{max}" # 应该是 88
 
+arr.each_with_index do |i, j|
+  puts i
+  puts j
+end
diff --git a/17-array-stats.rb b/17-array-stats.rb
index 0af81bb..b6e5aae 100644
--- a/17-array-stats.rb
+++ b/17-array-stats.rb
@@ -1,9 +1,9 @@
 # 使用者不断输入数字存进 Array，最后输出总和、平均、最大值、最小值
 
 arr = []
-
-while (true)
-  print "请输入数字，结束请直接按 Enter: "
+sum = 0
+loop do
+  print '请输入数字，结束请直接按 Enter: '
   user_input = gets
   if user_input == "\n"
     break
@@ -14,7 +14,13 @@
 
 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
+arr.each do |i|
+  sum += i.to_i
+end
+
+avr = (sum / arr.length).to_f
+
+puts "总和是 #{sum}"
+puts "平均是 #{avr}"
+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..a325fe7 100644
--- a/18-square.rb
+++ b/18-square.rb
@@ -2,9 +2,13 @@
 
 arr = []
 
-print "请输入数字 N，然后按 Enter: "
+print '请输入数字 N，然后按 Enter: '
 n = gets
-
+i = 0
 # ...
-
-puts arr.to_s
\ No newline at end of file
+loop do
+  break if i >= n.to_i
+  arr.push(i * i)
+  i += 1
+end
+puts arr.to_s
diff --git a/19-filter.rb b/19-filter.rb
index ef7e515..3472559 100644
--- a/19-filter.rb
+++ b/19-filter.rb
@@ -1,9 +1,14 @@
 # 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)
-  #...
+  # ...
+  evens = []
+  arr.each do |i|
+    odds.push(i) if i.even?
+  end
+  evens
 end
 
-arr =  [7, 68, 42, 46, 9, 91, 77, 46, 86, 1]
+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..ee5dc69 100644
--- a/20-sorting.rb
+++ b/20-sorting.rb
@@ -2,10 +2,14 @@
 # Hint: 可用 arr.sort 排序，和 arr.uniq 去除重复
 
 def filter_even(arr)
-  #...
+  # ...
+  evens = []
+  arr.each do |i|
+    evens.push(i) if i.even?
+  end
+  evens.sort.uniq
 end
 
-arr =  [7, 68, 42, 46, 9, 91, 77, 46, 86, 1]
+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).to_s # 应该是 [42, 46, 68, 86]
diff --git a/21-selection-sort.rb b/21-selection-sort.rb
index e5e7eae..c1579b4 100644
--- a/21-selection-sort.rb
+++ b/21-selection-sort.rb
@@ -2,11 +2,23 @@
 # https://zh.wikipedia.org/wiki/选择排序
 
 def selection_sort(arr)
-  #...
+  min = 0
+  tmp = 0
+  j = 0
+  for i in 0..(arr.length - 1)
+    min = i
+    for j in (i + 1)..(arr.length - 1)
+      min = j if arr[min] > arr[j]
+    end
+    tmp = arr[min]
+    arr[min] = arr[i]
+    arr[i] = tmp
+  end
+  arr.to_s
 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..dae6b92 100644
--- a/22-missing.rb
+++ b/22-missing.rb
@@ -1,9 +1,13 @@
 # 给定一阵列内含数字，请输出 0~9 中不见的数字
 
 def find_missing(arr)
-  # ...
+  miss = []
+  for i in 0..9
+    miss.push(i) unless arr.include?(i)
+  end
+  miss
 end
 
-answer = find_missing( [2,2,1,5,8,4] )
+answer = find_missing([2, 2, 1, 5, 8, 4])
 
 puts answer.to_s # 应该是 [0,3,6,7,9]
diff --git a/23-hash-max.rb b/23-hash-max.rb
index 6fb227e..d145521 100644
--- a/23-hash-max.rb
+++ b/23-hash-max.rb
@@ -2,18 +2,19 @@
 
 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,
-  "d" => 80,
-  "e" => 10
+  'a' => 71,
+  'b' => 38,
+  'c' => 21,
+  'd' => 80,
+  'e' => 10
 }
 
 answer = find_max(h)
 
 puts "有最大 value 的是 #{answer}" # 应该是 d
-
-
diff --git a/24-hash-even.rb b/24-hash-even.rb
index 9da9605..ef8fd05 100644
--- a/24-hash-even.rb
+++ b/24-hash-even.rb
@@ -1,21 +1,22 @@
 # 给定一 Hash，输出 value 是偶数的 keys
 
 def find_even_keys(hash)
-
+  evens = []
   # ... (请回传一个数组)
-
+  hash.each do |key, value|
+    evens.push(key) if value.even?
+  end
+  evens
 end
 
 h = {
-  "a" => 71,
-  "b" => 38,
-  "c" => 21,
-  "d" => 80,
-  "e" => 10
+  'a' => 71,
+  'b' => 38,
+  'c' => 21,
+  'd' => 80,
+  'e' => 10
 }
 
 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..f549de3 100644
--- a/25-hash-count.rb
+++ b/25-hash-count.rb
@@ -5,14 +5,18 @@ def count(arr)
 
   arr.each do |i|
     # ...
+    h[i] = if h.keys.include?(i)
+             h[i] + 1
+           else
+             1
+           end
   end
 
-  return h # 回传一个 hash
+  h # 回传一个 hash
 end
 
-arr =  ["a", "d", "d", "c", "b", "c", "c", "c", "d", "d", "e", "e", "e", "d", "a", "c", "e", "a", "d", "e"]
+arr =  %w(a d d c b c c c d d e e e d a c e a d e)
 
 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..e2b1b42 100644
--- a/26-hash-filter.rb
+++ b/26-hash-filter.rb
@@ -1,20 +1,20 @@
 # 给定一个数组包含 Hash，请过滤和排序
 
 arr = [
-  { "name" => "Peter", "age" => 30 },
-  { "name" => "John", "age" => 15 },
-  { "name" => "David", "age" => 45 },
-  { "name" => "Steven", "age" => 22 },
-  { "name" => "Vincent", "age" => 6 },
+  { 'name' => 'Peter', 'age' => 30 },
+  { 'name' => 'John', 'age' => 15 },
+  { 'name' => 'David', 'age' => 45 },
+  { 'name' => 'Steven', 'age' => 22 },
+  { 'name' => 'Vincent', 'age' => 6 }
 ]
 
-# ....
+arr.delete_if { |item| item['age'] < 18 }.sort_by! { |h| h['age'] }
 
-puts "所有成年人，并由小到大: _________"
+puts "所有成年人，并由小到大: #{arr}"
 
 # 答案应该是
-#[
+# [
 #  { "name" => "Steven", "age" => 22 },
 #  { "name" => "Peter", "age" => 30 },
 #  { "name" => "David", "age" => 45 }
-#]
+# ]
diff --git a/27-class.rb b/27-class.rb
index 8cec2c9..2f2f27d 100644
--- a/27-class.rb
+++ b/27-class.rb
@@ -1,16 +1,18 @@
 class Person
-  # ...
+  attr_accessor :first_name
+  attr_accessor :last_name
+
+  def greet
+    puts "Hello, #{@first_name} #{@last_name}"
+  end
 end
 
 p1 = Person.new
-p1.first_name = "Peter"
-p1.last_name = "Wang"
+p1.first_name = 'Peter'
+p1.last_name = 'Wang'
 p1.greet # 输出 "Hello, Peter Wang"
 
 p2 = Person.new
-p2.first_name = "William"
-p2.last_name = "Zhang"
+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..a29b415 100644
--- a/28-word-count.rb
+++ b/28-word-count.rb
@@ -1,5 +1,15 @@
 # 请打开 wordcount.txt，计算每个单字出现的次数
 
-doc = File.read("wordcount.txt")
+doc = File.read('wordcount.txt')
+arr = (doc.delete '.,').split(' ')
+count = {}
+arr.each do |word|
+  count[word] = if count.keys.include?(word)
+                  count[word] + 1
+                else
+                  1
+                end
+end
 
+puts count
 # ...
diff --git a/29-todos.rb b/29-todos.rb
index 0bddde2..a917d44 100644
--- a/29-todos.rb
+++ b/29-todos.rb
@@ -1,33 +1,55 @@
 # 简易 Todo 代办事项应用
 
-text = File.read("todos.txt")
+def readfile(filename)
+  todos = []
+  text = File.read(filename)
+  text.each_line do |line|
+    todos << line.chomp
+  end
+  todos
+end
 
-todos = []
-text.each_line do |line|
-  todos << line.chomp
+def print_todos(todos)
+  todos.each_with_index do |todo, index|
+    puts "#{index}: #{todo}"
+  end
 end
 
-todos.each_with_index do |todo, index|
-  puts "#{index}: #{todo}"
+def refresh_file(_filename)
+  todos = readfile('todos.txt')
+  print_todos(todos)
 end
 
-while (true)
-  print "请输入指令 1. add 2. remove 3. save，然后按 Enter: "
+FILE_NAME = 'todos.txt'.freeze
+
+loop do
+  refresh_file(FILE_NAME)
+
+  print '请输入指令 1. add 2. remove 3. save，然后按 Enter: '
   command = gets.chomp
 
-  if command == "add"
-    print "请输入代办事项: "
-    # ...
-  elsif command == "remove"
-    print "请输入要删除的编号: "
+  if command == 'add'
+    print '请输入代办事项: '
+    new_item = gets.chomp
+    File.open('todos.txt', 'a') do |f|
+      f.puts(new_item)
+    end
+  elsif command == 'remove'
+    print '请输入要删除的编号: '
     # ...
-  elsif command == "save"
-    puts "存盘离开"
-
+    del_index = gets.chomp.to_i
+    todos = readfile('todos.txt')
+    File.open('todos.txt', 'w') do |f|
+      todos.each_with_index do |line, index|
+        f.puts(line) unless index == del_index
+      end
+    end
+  elsif command == 'save'
+    refresh_file(FILE_NAME)
+    puts '存盘离开'
     # ...
-    break;
+    break
   else
-    puts "看不懂，请再输入一次"
+    puts '看不懂，请再输入一次'
   end
 end
-
diff --git a/todos.txt b/todos.txt
index 4757e85..d0ed9b6 100644
--- a/todos.txt
+++ b/todos.txt
@@ -1,4 +1,7 @@
-Buy book
-Go Shopping
-Walk
-Gogo
+first
+second
+third
+forth
+fifth
+sixth
+end