diff --git a/01-hello.rb b/01-hello.rb
index e0e7bbf..29a8257 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..3775704 100644
--- a/03-triangle.rb
+++ b/03-triangle.rb
@@ -1,11 +1,11 @@
 # 题目: 使用者输入直角三角形的宽和高，输出三角形的面积
 
 print "请输入直角三角形的高，然后按 Enter: "
-a = gets
+a = gets.to_i
 
 print "请输入直角三角形的底边，然后按 Enter: "
-b = gets
+b = gets.to_i
 
 # .....
 
-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: #{(b * a)/2}"
diff --git a/04-pizzas.rb b/04-pizzas.rb
index 4c2521f..ee7257e 100644
--- a/04-pizzas.rb
+++ b/04-pizzas.rb
@@ -1,12 +1,15 @@
 # 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
+a = pizzas
+b = people
+
+puts "每人可分得几片: #{ a/b } 片"
+puts "还剩下几片: #{ a%b } 片"
diff --git a/05-bmi.rb b/05-bmi.rb
index 67efdff..8b9ea51 100644
--- a/05-bmi.rb
+++ b/05-bmi.rb
@@ -5,13 +5,26 @@
 # 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
 
 # .....
 
-puts "您的 BMI 是: _________"
+a = weight
+b = height
+BMI = (a/(b*b))
 
-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: #{(a/(b*b))}"
+
+print "您的 BMI 结果是: "
+"#{
+if BMI < 18.5
+  puts "过轻"
+elsif BMI >= 24
+  puts "过重"
+else
+  puts "正常"
+end
+}"
diff --git a/06-interger-positive.rb b/06-interger-positive.rb
index a240f5f..ae3edce 100644
--- a/06-interger-positive.rb
+++ b/06-interger-positive.rb
@@ -2,9 +2,26 @@
 
 
 print "请输入一个整数，然后按 Enter: "
-x = gets
+x = gets.to_i
 
 # ....
 
-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
+print "这个数是: "
+"#{
+if x > 0
+  puts "正数"
+elsif x == 0
+  puts "零"
+else x < 0
+  puts "负数"
+end
+}"
+
+print "这个数是: "
+"#{
+if x%2 == 0
+  puts "偶数"
+else
+  puts "奇数"
+end
+}"
diff --git a/07-abcde.rb b/07-abcde.rb
index 5d0c8c3..9c0862d 100644
--- a/07-abcde.rb
+++ b/07-abcde.rb
@@ -9,14 +9,33 @@
 #     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
+print "结果是:"
+"#{
+if x < 0
+  puts "A"
+else x < 0
+  if y > 0
+    if z > 0
+      puts "B"
+    else z < 0
+      puts "C"
+    end
+  else y < 0
+    if z > 0
+      puts "D"
+    else z < 0
+      puts "E"
+    end
+  end
+end
+}"
diff --git a/08-find-max.rb b/08-find-max.rb
index 9e6e643..4957caa 100644
--- a/08-find-max.rb
+++ b/08-find-max.rb
@@ -1,14 +1,24 @@
 # 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
+print "最大的数是: "
+"#{
+if (x > y) && (y > z)
+  puts "#{x}"
+elsif (y > x) && (x > z)
+  puts "#{y}"
+else (z > x) && (x > y)
+  puts "#{z}"
+end
+}
+"
diff --git a/09-function.rb b/09-function.rb
index b1f922d..d1e26af 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)
-  # ....
+  (b * a)/2
 end
 
 print "请输入直角三角形的高，然后按 Enter: "
-a = gets
+a = gets.to_i
 
 print "请输入直角三角形的底边，然后按 Enter: "
-b = gets
+b = gets.to_i
 
 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..a558ceb 100644
--- a/10-function.rb
+++ b/10-function.rb
@@ -1,19 +1,26 @@
 # 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)
+  if x > y && y > z
+    return x
+  elsif y > x && x > z
+    return y
+  else z > x && x > y
+    return z
+  end
 end
 
 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
 
 # ....
 
 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..fb8f319 100644
--- a/11-seven.rb
+++ b/11-seven.rb
@@ -2,8 +2,9 @@
 
 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..820b1c5 100644
--- a/12-sum-even.rb
+++ b/12-sum-even.rb
@@ -4,10 +4,11 @@
 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..36e2ffa 100644
--- a/13-nn.rb
+++ b/13-nn.rb
@@ -1,11 +1,15 @@
 # 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 = 1
 
+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..ea5c97a 100644
--- a/14-prime.rb
+++ b/14-prime.rb
@@ -1,7 +1,16 @@
 # 输入一个数字 N，请检查是不是质数
 
 def is_prime(n)
-# ....
+  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: "
diff --git a/15-guess-number.rb b/15-guess-number.rb
index 48f9dca..8096bf7 100644
--- a/15-guess-number.rb
+++ b/15-guess-number.rb
@@ -4,14 +4,18 @@
 
 while (true)
   print "请猜一个 0~99 的数字 N，然后按 Enter: "
-  n = gets
+  n = gets.to_i
 
   #puts "太低了，再猜一次"
   #puts "太高了，再猜一次"
 
-  if n.to_i == target
+  if n == target
     puts "恭喜猜中啦! "
     break
+  elsif n > target
+    puts "太高了，再猜一次"
+  else n < target
+    puts "太低了，再猜一次"
   end
-
-end
\ No newline at end of file
+  
+end
diff --git a/16-array-sum.rb b/16-array-sum.rb
index 9b4910b..efbccff 100644
--- a/16-array-sum.rb
+++ b/16-array-sum.rb
@@ -1,11 +1,18 @@
 # 给定一阵列内含数字，输出最大值
 
 def find_max(array)
-  #....
+  m = 0
+
+  array.each do |i|
+    if m < i
+      m = i
+    end
+  end
+
+  return m
 end
 
 arr = [8, 12, 36, 53, 9, 75, 3, 71, 59, 88]
 
 max = find_max(arr)
 puts "Max is #{max}" # 应该是 88
-
diff --git a/17-array-stats.rb b/17-array-stats.rb
index 0af81bb..56b4a6d 100644
--- a/17-array-stats.rb
+++ b/17-array-stats.rb
@@ -14,7 +14,18 @@
 
 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
+def find_sum(array)
+  sum = 0
+  array.each do |i|
+    sum = sum + i
+  end
+
+  return sum
+end
+
+sum = find_sum(arr)
+
+puts "总和是 #{sum} "
+puts "平均是 #{sum / arr.size} "
+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..a4c1eb5 100644
--- a/18-square.rb
+++ b/18-square.rb
@@ -3,8 +3,15 @@
 arr = []
 
 print "请输入数字 N，然后按 Enter: "
-n = gets
+n = gets.to_i
 
 # ...
 
-puts arr.to_s
\ No newline at end of file
+x = 0
+while (x <= n-1)
+  y = x * x
+  arr << y
+  x += 1
+end
+
+puts arr.to_s
diff --git a/19-filter.rb b/19-filter.rb
index ef7e515..6f20711 100644
--- a/19-filter.rb
+++ b/19-filter.rb
@@ -1,9 +1,17 @@
 # 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)
-  #...
+  arr_even = []
+
+  arr.each do |i|
+    if i % 2 == 0
+      arr_even.push(i)
+    end
+  end
+
+  arr_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..fb986b6 100644
--- a/20-sorting.rb
+++ b/20-sorting.rb
@@ -2,10 +2,18 @@
 # Hint: 可用 arr.sort 排序，和 arr.uniq 去除重复
 
 def filter_even(arr)
-  #...
+  arr_even = []
+
+  arr.each do |i|
+    if i % 2 == 0
+      arr_even.push(i)
+    end
+  end
+
+  arr_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).uniq.sort.to_s # 应该是 [42, 46, 68, 86]
diff --git a/21-selection-sort.rb b/21-selection-sort.rb
index e5e7eae..506a706 100644
--- a/21-selection-sort.rb
+++ b/21-selection-sort.rb
@@ -2,11 +2,19 @@
 # https://zh.wikipedia.org/wiki/选择排序
 
 def selection_sort(arr)
-  #...
+  return arr if arr.length == 0
+  (0..arr.length-1).each do |i|
+    min, index = arr[i], i
+    (i+1..arr.length-1).each do |j|
+      min, index = arr[j], j if arr[j] < min
+      arr[i], arr[index] = arr[index], arr[i]
+    end
+  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..90b3ec6 100644
--- a/22-missing.rb
+++ b/22-missing.rb
@@ -1,7 +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)
-  # ...
+  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..3755a0e 100644
--- a/23-hash-max.rb
+++ b/23-hash-max.rb
@@ -1,7 +1,9 @@
 # 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 = {
@@ -15,5 +17,3 @@ def find_max(hash)
 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..31a9cd4 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)
-
+  even = []
+  hash.each do |key, value|
+    even << key if value % 2 == 0
+  end
+  even
 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..8bf8530 100644
--- a/26-hash-filter.rb
+++ b/26-hash-filter.rb
@@ -10,7 +10,23 @@
 
 # ....
 
-puts "所有成年人，并由小到大: _________"
+h = []
+arr.each do |a|
+  if a["age"] > 18
+    h << a
+  end
+  h
+end
+
+(0..h.length-1).each do |i|
+  min, index = h[i], i
+  (i+1..h.length-1).each do |j|
+    min, index = h[j], j if h[j]["age"] < min["age"]
+    h[i], h[index] = h[index], h[i]
+  end
+end
+
+puts "所有成年人，并由小到大: #{h}"
 
 # 答案应该是
 #[
diff --git a/27-class.rb b/27-class.rb
index 8cec2c9..607b10a 100644
--- a/27-class.rb
+++ b/27-class.rb
@@ -1,5 +1,9 @@
 class Person
-  # ...
+  attr_accessor :first_name, :last_name
+
+  def greet
+    puts "Hi, #{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..bd96762 100644
--- a/28-word-count.rb
+++ b/28-word-count.rb
@@ -3,3 +3,18 @@
 doc = File.read("wordcount.txt")
 
 # ...
+
+word_count = Hash.new(0)
+doc.each_line do |line|
+  line = line.gsub(/[,'".]/,'')
+  words = line.split
+  words.each do |word|
+    word_count[word] += 1
+  end
+end
+
+puts '每个单词出现的频数为：'
+
+word_count.each do |key, value|
+  puts "#{key} #{value}"
+end
diff --git a/29-todos.rb b/29-todos.rb
index 0bddde2..875ae10 100644
--- a/29-todos.rb
+++ b/29-todos.rb
@@ -17,17 +17,27 @@
 
   if command == "add"
     print "请输入代办事项: "
-    # ...
+    n = gets.chomp
+    todos << n
+    todos.each_with_index do |todo, index|
+      puts "#{index}: #{todo}"
+    end
   elsif command == "remove"
     print "请输入要删除的编号: "
-    # ...
+    todos.delete_at(gets.chomp.to_i)
+    todos.each_with_index do |todo, index|
+      puts "#{index}: #{todo}"
+    end
   elsif command == "save"
     puts "存盘离开"
-
-    # ...
+    File.open("todos.txt", "w+") do |f|
+        todos.each do |todo|
+          f << todo
+          f << "\n"
+        end
+      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..ebb88ea 100644
--- a/todos.txt
+++ b/todos.txt
@@ -2,3 +2,4 @@ Buy book
 Go Shopping
 Walk
 Gogo
+Car