If the cost price of 12 pens is equal to the selling price of 8 pens, the gain percent is:

A. 25%
B. 33 1/3 %
C. 50%
D. 66 2/3 %

Explanation:

Let C.P. of each pen be Re. 1.

Then, C.P. of 8 pens = Rs. 8; S.P. of 8 pens = Rs. 12.
Gain % = 4/8 * 100 = 50%