Data Sufficiency

Representation in a local community board is based on the community's population, with 25 board members representing the first 500,000 people, and each additional board member representing an additional 30,000 people. Is the population of the town less than 500,000?

(1) There were 23 members on the community board.
(2) If the population were three times as large, the community board would have had 51 members.

Source: Princeton

Answer is D

Why is A sufficient?
I was thrown off by the condition that each member after the first 25 represents 30,000 people, since this condition is not met in A, I dismissed it

p<500,000?
a)25 members represent first 500,000. and only 23 members are present, p<500,000
Sufficient
b)with 51 members, we can find changed population and thus divide by 3 ans determine actual.
IMO D