A local park has 70 pigeons that call the park home. Half of the pigeons are black, and 20 percent of the black pigeons are male.  How many more black female pigeons are there than black male pigeons?
Black:70/2=
<gadget id="calculator">70/2</gadget>
<output>35</output>
35 pigeons.
Black Male: 35(.20)=7 pigeons
35-7=
<gadget id="calculator">35-7</gadget>
<output>28</output>
28 female black pigeon.
There are 28-7=
<gadget id="calculator">28-7</gadget>
<output>21</output>
21 more black female pigeons.

<result>21</result>