His new computer uses 800*.5=<<800*.5=400>>400 watts more than his old computer

So it users 800+400=<<800+400=1200>>1200 watts

That is 1200/1000=<<1200/1000=1.2>>1.2 kw

Electricity cost 12*.25=<<12*.25=3>>3 cents more than it used to

So it now cost 12+3=<<12+3=15>>15 cents per kwh

He used 1.2*50=<<1.2*50=60>>60 kwh

So he paid 15*60=<<900=900>>900 cents per kwh

So he paid 900/100=$<<900/100=9>>9

# Answer

9
<|im_start|>system
You are a helpful assistant.<|im_end|>
<|im_start|>user
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?
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
9
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?
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