GMATPrep - folks at a seminar

[AleksandrM]

At a two-day seminar, 90 percent of those registered attended the seminar on the first day. What percentage of those registered did not attend the seminar one either day?

(1) A total of 1,000 people registered for the two-day seminar.

(2) Of those registered, 80 percent attended the seminar on the second day.

[amitansu]

Ans C here ?

Venn diagram's application.

[VP_Tatiana]

The answer here would be E.

1 gives us no relevant information whatsoever. We only care about percents, but not about actual number of participants.

Using #2, we could have several possibilities. The 80% that went on the second day could all be people that went on the first day, in which case 90% went at least one day. Or, we could have the case where ALL of the people that skipped the first day were part of the 80% that went the second day. In that case, 100% went to at least one day.

Thus, #2 does not give us sufficient information and the answer is E.