If the selling price of 50 books is equal to the cost price of 40 books, then the loss or gain percent is:
Pick one
A) 10  B) 30  C) 20  D) 40  E) 50
C   20%   Let C.P. of each books be $ 1.   Then, C.P. of 50 books= $50;   S.P. of 50 books = $40.   Loss % = 10/50 * 100= 
<gadget id="calculator">10/50 * 100</gadget>
<output>20</output>
20%
<result>C</result>
If the selling price of 50 books is equal to the cost price of 40 books, then the loss or gain percent is: