Krishna purchased a number of articles at Rs. 10 for each and the same number for Rs. 14 each. He mixed them together and sold them for Rs. 13 each. Then his gain or loss percent is = ?

Let article purchased be 1
1 articale = Rs. 10
1 articale = Rs. 14
CP of 2 article = 10 + 14 = Rs. 24
CP of 1 article = $$\frac{{24}}{2}$$ = Rs. 12
SP of 1 article = Rs. 13
Profit = 13 - 12 = Rs. 1
$$\eqalign{ & {\text{Profit}}\% = \frac{1}{{12}} \times 100 \cr & \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = \frac{{25}}{3} \cr & \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\, = 8\frac{1}{3}\% \cr} $$