A farmer is growing corn. For every 4 seeds he plants, he gets one ear of corn, that he can sell for $.1. It costs $.5 for a bag with 100 seeds. If he makes $40 in profit, how many ears did he sell?
A single seed costs $.005 because .5 / 100 = 
<gadget id="calculator">.5/100</gadget>
<output>0.005</output>
.005.
It costs $.02 cents to grow an ear of corn because .005 x 4 = 
<gadget id="calculator">.005*4</gadget>
<output>0.02</output>
.02.
On each ear of corn he makes $.098 profit because .1 - .02 = .08.
He sold 500 ears because 40 / .08 = 
<gadget id="calculator">40/.08</gadget>
<output>500</output>
500.

<result>500</result>