A girl scout sells 3 boxes of cookies during week 1. She has a goal to sell twice as many cookies each week as she did the week before. If she succeeds in doing this during weeks 2, 3, 4, and 5, how many boxes will she sell all together?
This is a geometric sequence with common ratio r = 2. So in second week she sells 3*2 = 6 cookies. so the number of cookies she sell over the 5 weeks is
