There are 480 zombies in the shopping mall. If the number of zombies doubled every day, how many days ago were there less than 50 zombies in the mall?
First find how many zombies there were one day ago: 480 zombies / 2 = 
<gadget id="calculator">480/2</gadget>
<output>240</output>
240 zombies.
Then find how many zombies there were two days ago: 240 zombies / 2 = 
<gadget id="calculator">240/2</gadget>
<output>120</output>
120 zombies.
Then find the number of zombies there were three days ago: 120 zombies / 2 = 
<gadget id="calculator">120/2</gadget>
<output>60</output>
60 zombies.
Then find the number of zombies there were four days ago: 60 zombies / 2 = 
<gadget id="calculator">60/2</gadget>
<output>30</output>
30 zombies, which is less than 50, so there were less than 50 zombies 4 days ago.

<result>4</result>