Peter has to walk 2.5 miles to get to the grocery store. If it takes him 20 minutes to walk one mile and he has walked 1 mile already, how many more minutes does he have to walk to reach it?
Peter has to walk a remaining 2.5 total miles - 1 mile completed = 
<gadget id="calculator">2.5-1</gadget>
<output>1.5</output>
1.5 miles remaining.
It will take him another 20 minutes * 1.5 miles remaining = 
<gadget id="calculator">20*1.5</gadget>
<output>30</output>
30 minutes to get to the grocery store.

<result>30</result>