Ruby assignment operators on strings

numbers.txt

[6] pry(main)> f *= 9
=> "rubygemsrubygemsrubygemsrubygemsrubygemsrubygemsrubygemsrubygemsrubygems"
[7] pry(main)> f /= 9
NoMethodError: undefined method `/' for #<String:0x0000000148ad40>
from (pry):7:in `__pry__'
[8] pry(main)> f -= 9
NoMethodError: undefined method `-' for #<String:0x0000000148ad40>
Did you mean?  -@
from (pry):8:in `__pry__'
[9] pry(main)> f += 9
TypeError: no implicit conversion of Fixnum into String
from (pry):9:in `+'
[10] pry(main)>

strings.txt

ken@kenny:~$ pry
[1] pry(main)> f = 'ruby'
=> "ruby"
[2] pry(main)> f *= 'gems'
TypeError: no implicit conversion of String into Integer
from (pry):2:in `*'
[3] pry(main)> f /= 'gems'
NoMethodError: undefined method `/' for "ruby":String
from (pry):3:in `__pry__'
[4] pry(main)> f += 'gems'
=> "rubygems"
[5] pry(main)> f -= 'gems'
NoMethodError: undefined method `-' for "rubygems":String
Did you mean?  -@
from (pry):5:in `__pry__'
[6] pry(main)>