There are 13 3-year-olds, 20 4-year-olds, 15 5-year-olds, and 22 six-year-olds at a particular Sunday school. If the 3 and 4-year-olds are in one class and the 5 and 6-year-olds are in another class, what is the average class size?
First find the total number of 3- and 4-year-olds: 13 kids + 20 kids = 
<gadget id="calculator">13+20</gadget>
<output>33</output>
33 kids.
Then find the total number of 5- and 6-year-olds: 15 kids + 22 kids = 
<gadget id="calculator">15+22</gadget>
<output>37</output>
37 kids.
Then add the two class sizes: 33 kids + 37 kids = 
<gadget id="calculator">33+37</gadget>
<output>70</output>
70 kids.
Then divide the number of kids by the number of classes to find the average class size: 70 kids / 2 classes = 
<gadget id="calculator">70/2</gadget>
<output>35</output>
35 kids/class.

<result>35</result>