Question below is from a top school exam year 2007
Now try a similar question:
The average cost of some math books in a box was $15 at first. To double the number of books in the box, a number of science books whose total cost is unknown are added to the box. The average cost of books in the box now is 20. Then, all math books are removed from the box. What is average cost of books in the box now?
(1) 15
(2) 20
(3) 25
(4) 30
(1) 15
(2) 20
(3) 25
(4) 30
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