Suppose that you ask three friends to go to the mall. Each one has a 0.80 chance of saying yes. What is the probability that at least one friend can go to the mall with you?

Question

mathmale · Answer

Since you have 3 friends, n=3.  Also, p=0.80.

"the probability that at least one friend can go to the mall with you" is 
the sum of P(1 friend can go) + P(2 friends can go) + P(3 friends can go).

Or, you could find the following:  1-P(0 friends can go) 

This is binomial probability.  Know the formula for that?  Or have you a table of binomial probabilities?