There were 50 people on the city bus. At the first stop, 15 people got off. At the next stop 8 people got off and 2 got on. At the third stop, 4 people got off and 3 people got on. How many people are on the bus after the third stop?
The bus started with 50 people - 15 who got off at the first stop = 
<gadget id="calculator">50-15</gadget>
<output>35</output>
35 people on the bus.
At the second stop, 35 people on the bus - 8 who got off = 
<gadget id="calculator">35-8</gadget>
<output>27</output>
27 people.
Then there were 27 people + 2 who got on = 
<gadget id="calculator">27+2</gadget>
<output>29</output>
29 people on the bus.
At the third stop, 29 people on the bus - 4 who got off = 
<gadget id="calculator">29-4</gadget>
<output>25</output>
25 people on the bus.
Then there were 25 people on the bus + 3 who got on = 
<gadget id="calculator">25+3</gadget>
<output>28</output>
28 people on the bus.

<result>28</result>