A couple's wedding reception had 180 people. The bride and groom had each invited 20 couples from their side of the family. The remaining guests were friends. How many friends attended the reception?
From the bride's side, 20 couples * 2 guests/couple = 
<gadget id="calculator">20*2</gadget>
<output>40</output>
40 guests attended.
From the groom's side, 20 couples * 2 guests/couple = 
<gadget id="calculator">20*2</gadget>
<output>40</output>
40 guests attended.
Therefore 180 guests - (40 guests + 40 guests) = 
<gadget id="calculator">180-(40+40)</gadget>
<output>100</output>
100 friends attended the reception.

<result>100</result>