Hi j_shreyans,

This DS question is based on some "average formula" concepts that can help you to answer this question without doing much work. However, if you're ever a bit unsure about a given Fact, you should TEST IT to be sure.

Here, we're told that there are 5 employees who averaged 16 vacation days last year. This means that 5(16) = 80 total vacation days were taken by these 5 employees. We're asked what the average was for these 5 employees THIS YEAR. Ultimately, the question is asking how many total vacation days were taken THIS YEAR by those same 5 people.

Fact 1: 3 employees had a 50% increase in vacation days and 2 employees had a 50% decrease.

This info seems problematic, since we don't know how many days each person had individually. The +50%/-50% could have a different effect when applied to each person.

Let's TEST Values:
Last year, if all 5 people had 16 vacation days each....
This year:
3 employees had 24 vacation days = 72 days
2 employees had 8 vacation days = 16 days
72 + 16 = 88 total vacation days this year

Last year, If 3 employees (who had +50% this year) had 20 days each and 2 employees (who had -50% this year) had 10 days each...
This year:
3 employees had 30 vacation days = 90 days
2 employees had 5 vacation days = 10 days
90 + 10 = 100 total vacation days this year
Fact 1 is INSUFFICIENT

Fact 2: 3 employees had 10 more days each and 2 employees had 5 fewer days each.

This information allows us to calculate the "net change" in vacation days...

Last year = 80 total vacation days
This year:
3 employees had 10 more days each = +30 vacation days
2 employees had 5 fewer days each = -10 vacation days
80 + 30 - 10 = 100 total vacation days
Fact 2 is SUFFICIENT

Final Answer: B

GMAT assassins aren't born, they're made,
Rich