Stephen ordered 2 large pizzas, both cut into 12 slices.  He ate 25% of the pizza.  His friend Pete ate 50% of the remaining pizza.  How many slices are left over?
He ordered 2 pizzas, each cut into 12 slices so that's 2*12 = 
<gadget id="calculator">2*12</gadget>
<output>24</output>
24 slices.
Stephen ate 25% of the pizza so he ate .25*24 = 
<gadget id="calculator">25*.01*24</gadget>
<output>6</output>
6 slices.
That leaves 24-6 = 
<gadget id="calculator">24-6</gadget>
<output>18</output>
18 slices
18 slices are left and Pete eats 50% of 18 slices so he eats 18*.50 = 
<gadget id="calculator">18*50*.01</gadget>
<output>9</output>
9 slices.
If there were 18 slices and Pete ate 9 slices then there are 18-9 = 
<gadget id="calculator">18-9</gadget>
<output>9</output>
9 slices left over.

<result>9</result>