Facebook According to Pew Research, 50% of adults and 75% of teenagers were using a social networking site in early 2012. Most of that activity was on Facebook. Let’s assume these probabilities apply...

Facebook According to Pew Research, 50% of adults and 75% of teenagers were using a social networking site in early 2012. Most of that activity was on Facebook. Let’s assume these probabilities apply strictly to Facebook (after all, MySpace is empty, right?) Among a group of 10 people, what’s the probability that

a) at least one of the people was not on Facebook if they were all adults?

 b) at least one of the people was not on Facebook if they were all teenagers?

c) at least one of the people was not on Facebook if half were teenagers?