Alice's white water rafting class is composed of 40 students and 10 instructors, including herself.  She has 20 life vests on hand.  20% of her students are bringing life vests.  How many more life vests will Alice need to get so that entire class has one?
How many students will bring their own life vests? ** 20% of her 40 students will bring their own life vest so .20*40 = <<.20*40=8>>8 students will bring their life vests
How many life vests does Alice have? ** Alice has 20 life vests and 8 students will bring there's so that's 20+8 = <<20+8=28>>28 life vests
How many people are in the class? ** There are 40 students and 10 instructors total so that's 40+10 = <<40+10=50>>50 people in the class
How many more life vards will Alice need to get so that entire class has one? ** If there are 28 life vests and she has 50 people then she needs to find 50-28 = 22 more life vests
#### 22