A girl scout was selling boxes of cookies. In a month, she sold both boxes of chocolate chip cookies ($1.25 each) and boxes of plain cookies ($0.75 each). Altogether, she sold 1,585 boxes for a combined value of $1,588.25. How many boxes of plain cookies did she sell?	Select:
A) 0	B) 233	C) 500	D) 695	E) 786
Let #plain cookies sold be X then #chocolate cookies = (total cookies-X)   Equating for X   (0.75)*X +(1.25)*(1585-X)=1588.25   =&gt;x=786   First get the difference of the revenue to the number of boxes.   1588.25-1585= 
<gadget id="calculator">1588.25-1585</gadget>
<output>3.25</output>
3.25   Now you know that the difference between plain cookies boxes and chocolate cookies boxes is small.   We now divide the revenue by two.   1588.25/2=~794   Because the difference between the possible answers is big, this leaves us with choice 786.
<result>E</result>
A girl scout was selling boxes of cookies. In a month, she sold both boxes of chocolate chip cookies ($1.25 each) and boxes of plain cookies ($0.75 each). Altogether, she sold 1,585 boxes for a combined value of $1,588.25. How many boxes of plain cookies did she sell?