sets

[AJWILL]

In a certain locality, 25% of the residents read newspaper A and 20 percent of the residents read newspaper B. What percent of the residents in that locality read neither newspaper A nor newspaper B?
(1) 4/5 of the residents who read newspaper A also read newspaper B.
(2) Total number of residents in locality are more than 500.

[eagleeye]

In a certain locality, 25% of the residents read newspaper A and 20 percent of the residents read newspaper B. What percent of the residents in that locality read neither newspaper A nor newspaper B?
(1) 4/5 of the residents who read newspaper A also read newspaper B.
(2) Total number of residents in locality are more than 500.

We know that total number = 100
Now we are given that 25 read A and 20 read B.
We need to find the ones who don't read A or B. Lets call them as totaling N.
Let's call people who read both common readers as totaling C.

Now using set theory/venn diagrams, we know that
Total = A + B - C + N
100 = 25 + 20 -C + N
So if we know either of C or N, we have sufficiency.

With that in mind, let's look at the options:

(1) 4/5 of the residents who read newspaper A also read newspaper B.
We are told that C = 4/5*A = 4/5*25 = 20. Hence we can find N using the equation above. Sufficient.

(2) Total number of residents in locality are more than 500.
Who cares about the total number. We are interested in percentages. Insufficient.

A is correct.