My younger son and I are in the middle of talking about percents. This morning the topic at hand was questions like – what number is 20% more than 50?
It was interesting to me to see the difference in approach that my son had to problems involving integers, fractions, and decimals. It is easy for me to forget how different these representations of numbers are to kids.
Integers first – what is 20% more than 70?
Now fractions – what is 30% less than 1/5?
Finally decimals – what is 10% more than 3.4
I don’t know at what level of mathematical development integers, fractions, and decimals all meld into numbers. It sure is easy for me to forget that they don’t appear to be the same things to a kid.
Mike's Math Page 
And whose fault could that possibly be ?
I think I agree with Howard’s implied point: different representations of numbers only come to be viewed as the same when that point is taught explicitly. It can actually be a very interesting conversation to discuss when different forms are used and why.