Correct Answer: INR 255

Solution : Let the cost price of the 1st article be $x$ and the 2nd article be $y$
According to the question,
(100 – 15)% × $x$ = (100 – 25)% × $y$
⇒ $85\% × x = 75\% × y$
⇒ $\frac{x}{y} = \frac{15}{17}$
Let the $x$ and $y$ value as $15a$ and $17a$ respectively.
According to the question,
⇒ $15a + 17a = 640$
⇒ $32a = 640$
⇒ $a = 20$
Thus, $15a = 300$
The cost price of 1st article = INR 300
The selling price of the 1st article = 85% of 300
= $\frac{85}{100}\times300$
= 255
Hence, the correct answer is INR 255.