How do I solve this AP Chemistry problem?

Question

B. A 10.00mL sample of the concentrated nitric acid was diluted with water to a total volume of 500.00mL. Then 25.00mL of the diluted acid was tritrated with the standardized NaOH solution prepared in part A. The equivalence point was reached after 28.35mL of the base had been added. Calculate the molarity of the concentrated nitric acid.

Answer 1

The balanced equation for this reaction is:

HNO3 + NaOH ==> NaNO3 + H2O

We need to know the concentration of the standardized NaOH that was prepared in part A.  Then, find moles NaOH in 28.35 ml (0.02835 L).  That will be equal to moles HNO3 in 25 ml of the diluted acid solution.  Finally, the molarity of the concentrated nitric acid can be found by moles/0.025 L and then multiplying that value by 50 to account for the dilution factor of 10.00 ml diluted to 500.00 ml