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?
20% of her 40 students will bring their own life vest so .20*40 = 
<gadget id="calculator">.20*40</gadget>
<output>8</output>
8 students will bring their life vests.
Alice has 20 life vests and 8 students will bring there's so that's 20+8 = 
<gadget id="calculator">20+8</gadget>
<output>28</output>
28 life vests.
There are 40 students and 10 instructors total so that's 40+10 = 
<gadget id="calculator">40+10</gadget>
<output>50</output>
50 people in the class.
If there are 28 life vests and she has 50 people then she needs to find 50-28 = 22 more life vests.

<result>22</result>