Hi,,
After posting last night I determined that 'pop' was a string by running:

   puts pop.class

I then found out about the .to_i method. After applying this my issue at 
least seems to be resolved. The post below at least confirms I'm on the 
right track, so thanks for that.

Jen.

On 19/03/11 23:26, Jeremy Bopp wrote:
> On 03/19/2011 06:16 PM, Jen wrote:
>> Hi John,
>>
>> I confess I don't know a lot of the technical stuff about class Fixnum,
>> as I've not really needed to until now.
> You should take a little time and learn a bit more detail about numbers
> in Ruby.  Expanding your knowledge about strings and the String class
> would also be a good idea so that you understand how the classes differ. :-)
>
>> Currently I am getting the value of 'pop' from the user with the
>> following code:
>>
>>    puts "please enter a population size"
>> pop = gets.chomp
> The gets method returns a String.  The chomp method is a method for
> String instances that also returns a String.  If the String represents a
> number, such as "1234", then you can convert that into a Fixnum or
> related number type by calling to_i on the String.  e.g.)
>
> the_number = pop.to_i
>
> -Jeremy
>