errors with respond_to? and inject

Hello,

This is my first post, and i hope i use the correct topic.
There are two errors i do not understand in the code below

I've commented out the line that don't work, and the line directly below
works just fine
Finally i put the errors when using the problematic lines

I do not see any errors in the commented line, if someone do i'll be
happy to understand what is wrong

thx in advance

Here is the code
----------------------------------------------------------------
class Item
  attr_reader :name, :price

  def initialize name, price
    @name, @price = name, price
  end

  def + item
#    price + item.price if item.respond_to? price #### 1
    price + item.price if item.is_a? Item
  end
end

class Items
  def initialize
    @items = []
  end

  def << item
    @items << item if item.is_a? Item
  end

  def price
    @items.collect { |i| i.price }.inject(:+)
#    @items.inject(:+) #### 2
  end
end

i = Items.new

i << Item.new('a', 1)
i << Item.new('b', 2)
i << Item.new('c', 3)

puts i.price
--------------------------------------------------------------
The errors
--------------------------------------------------------------
##### 1
./test2.rb:11:in `respond_to?': 1 is not a symbol (TypeError)
##### 2
./test2.rb:25:in `+': Item can't be coerced into Fixnum (TypeError)

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