math.random how to choose multiple random numbers?

So, i've tried to make a script where when a player joins, a ball appears. Everything is going out well except that the size doesn't randomize.

game.Players.PlayerAdded:connect(function(player)
    local ball = Instance.new("Part", workspace.Lobby)
    ball.Shape = Enum.PartType.Ball
    ball.Color = Color3.new(math.random(), math.random(), math.random())
    ball.Size = Vector3.new(math.random(7, 8, 9, 10), math.random(6, 7, 8, 9, 10), math.random(6, 7, 8, 9, 10))
    ball.Position = Vector3.new(0.5, 0.5, -0.5)
end)

what's the problem, the error says it has a wrong number of arrangements but i don't know what that means. How do i fix it?