Answer:
Part a.
Last year, there were 550 bison in the herd.
This year, there were 10% more than last year, that means this year were 110%. So,

So, this year were 605 bison in the herd.
Part b.
This year, there was a 10% decrease in population.
Last year, there were 550 bison in the hard. So, all this means that all 550 bison represents 90% of the last year. So,

As you can observe, part a and part b have different results, therefore, Noah is wrong.