The price of electricity went up by 25%.  John's old computer used 800 watts and his new computer uses 50% more.  If the old price of electricity was 12 cents per kilowatt-hour, how much does his computer cost, in dollars, to run for 50 hours?
His new computer uses 800*.5=
<gadget id="calculator">800*.5</gadget>
<output>400</output>
400 watts more than his old computer.
So it users 800+400=
<gadget id="calculator">800+400</gadget>
<output>1_200</output>
1200 watts.
That is 1200/1000=
<gadget id="calculator">1200/1000</gadget>
<output>6/5 = around 1.2</output>
1.2 kw.
Electricity cost 12*.25=
<gadget id="calculator">12*.25</gadget>
<output>3</output>
3 cents more than it used to.
So it now cost 12+3=
<gadget id="calculator">12+3</gadget>
<output>15</output>
15 cents per kwh.
He used 1.2*50=
<gadget id="calculator">1.2*50</gadget>
<output>60</output>
60 kwh.
So he paid 15*60=
<gadget id="calculator">900</gadget>
<output>900</output>
900 cents per kwh.
So he paid 900/100=$
<gadget id="calculator">900/100</gadget>
<output>9</output>
9.

<result>9</result>