There are 20 students in the class. Half of them play basketball. Two-fifths play volleyball and one-tenth play both basketball and volleyball.  How many students in this class do not play either game?
Half of the students are playing basketball, which means 20 / 2 = 
<gadget id="calculator">20/2</gadget>
<output>10</output>
10 students play basketball.
Two-fifths plays volleyball, which leaves us with 20 * 2/5 = 
<gadget id="calculator">20*2/5</gadget>
<output>8</output>
8 students.
One-tenth play both games, which means 20 * 1/10 = 
<gadget id="calculator">20*1/10</gadget>
<output>2</output>
2 students.
There are 10 + 8 = 
<gadget id="calculator">10+8</gadget>
<output>18</output>
18 students who play basketball or volleyball.
Among these 18 students, 2 of them are playing both games, so that means 18 - 2 = 
<gadget id="calculator">18-2</gadget>
<output>16</output>
16 students play only one of the two games.
So finally, 20 - 16 = 
<gadget id="calculator">20-16</gadget>
<output>4</output>
4 students do not play either game.

<result>4</result>