In a certain city, the ratio of the number of people who purchase newspaper X to the number of people who purchase newspaper Y is 7:1. What percent of the population purchases newspaper Y?
1- Twenty-seven percent of the population purchases neither newspaper X nor newspaper Y.
2- Seventy percent of the people who purchase newspaper Y also purchase newspaper X.
The answer can only be C
U = a + b + neither -ab
From 1, we can find a+b and none in terms of U, but we don't know ab. insuff.
From 2, we can fine ab but we can't find the rest.
Combining both of the above, we have a solution