Correct Answer: 16%

Solution : Cost price of the 1st article = Rs. 400
Selling price with a gain of 10% = $\frac{110}{100}\times400=440$
Cost price of the 2nd article = Rs. 600
Selling price with a gain of 20% = $\frac{120}{100}\times600=720$
Total cost price = 400 + 600 = 1000
Total selling price = 440 + 720 = 1160
Gain = selling price – cost price = 1160 – 1000 = 160
$\therefore$ Gain percentage $=\frac{\text{Gain}}{\text{cost price}}\times100=\frac{160}{1000}\times100
= 16\%$
Hence, the correct answer is 16%.