A bag of blue and green colored marbles has 25% green marbles, with a total of 40 marbles. how many green marbles need to be added to bring their percentage in the bag up to 40%?
Answers:
A) 4
B) 8
C) 12
D) 10
E) 15
A bag of 40 marbles which is 25% green marbles means we have 10 green marbles. To get a bag that is 40% green marbles, let's use this expression: (10 + x)/(40 + x) = 0.4 with x representing the amount of green marbles that must be added to get to 40%. The expression thus represents the new number of green marbles over the total new number of marbles in the bag and this fraction should equal 40%. only ten marbles need to be added, as  20/50= 
<gadget id="calculator"> 20/50</gadget>
<output>2/5 = around 0.4</output>
0.4 or 40%   choose 10
<result>D</result>
A bag of blue and green colored marbles has 25% green marbles, with a total of 40 marbles. how many green marbles need to be added to bring their percentage in the bag up to 40%?