Selling price of two articles $$ = 640$$ Rs. each Let cost price of article on which man gains $$20\%\ profit$$ be $$X$$ Rs
and another article on which man gains $$10\%\ profit$$ be $$Y$$ Rs.
Solving for first article on which man gains 20% profit
We know that, $$Selling\ price = Cost\ price + profit$$
$$\Rightarrow 640 = X + 20\%\ of\ X$$
$$\Rightarrow 640 = X+0.2X$$
$$\Rightarrow 640 = 1.2X$$
$$\Rightarrow X = \dfrac{640}{1.2}$$
$$\therefore X = \dfrac{1600}{3}\ Rs$$
Now, Solving for article on which man gains 10% profit
We know that, $$Selling\ price=Cost\ price+loss$$
$$\Rightarrow 640 = Y +10\%\ of\ Y$$
$$\Rightarrow 640 = Y + 0.1Y$$
$$\Rightarrow 640 = 1.1Y$$
$$\Rightarrow Y = \dfrac{640}{1.1}$$
$$\therefore Y = \dfrac{6400}{11}\ Rs$$
Now, $$Total\ Cost\ price = X + Y = \dfrac{1600}{3}+\dfrac{6400}{11}=\dfrac{17600+19200}{33} = \dfrac{36800}{33}\ Rs=1115.15\ Rs$$
and $$Total\ Selling\ price = 2\times640 = 1280\ Rs$$
Overall profit $$Selling\ price-Cost\ Price=1280-1115.15=164.85\ Rs$$
$$\therefore Profit\ percentage=\dfrac{profit\times100}{Cost\ price}=\dfrac{164.85\times100}{1115.15}=14.78\%$$