这里有一个无限循环：

until distance > 1000 do
  speed = Random.rand(5...15)
  distance = speed * 1
  time = time + 1
end

这个循环永远不会结束，因为distance可以得到的最大值是15，所以我认为你应该添加到distance，而不是替换它;儿子尝试使用+=而不是=：

until distance > 1000 do
  speed = Random.rand(5...15)
  distance += speed * 1
  time = time + 1
end

在每种情况下，所有循环也是如此。
如何保存最大速度并像我所做的那样在语句中返回它？
一种方法是添加另一个变量（例如max_speed），并在speed大于max_speed时为其分配speed值：

time = 0
distance = 0
max_speed = 0

until distance > 1000 do
  speed = Random.rand(5...15)
  max_speed = speed if speed > max_speed
  distance += speed * 1
  time = time + 1
end

puts "The maximum speed was #{max_speed} miles per hour"

另一种方法是使用数组（尽管我更喜欢第一种选择）：

speed = []

until distance > 1000 do
  speed << Random.rand(5...15)
  distance += speed.last * 1
  time = time + 1
end

puts "The maximum speed was #{speed.max} miles per hour"

实际上，您并没有对距离求和-距离永远不会超过1000

until distance > 1000 do
  speed = Random.rand(5...15)
  distance = speed * 1 # will never equal more than 15
  time = time + 1
end

你可能想

distance += speed * 1 # not sure why you're multiplying by 1 though

作为风格注解：不要像if/then语句那样使用case语句作为控制流。只使用它们来设置值，并将其他所有内容移出。这可以消除大量冗余代码。例如：

time = 0
distance = 0
until distance > 1000 do   
  speed = case vehicle
    when "1" then Random.rand(5...15)    #Bicycle
    when "2" then Random.rand(20...70)   #Car
    when "3" then Random.rand(400...600) #Plane
    end
  distance += speed * 1
  time = time + 1
end
puts "The number of hours it took to travel 1000 miles was #{time} hours"