Marked price of an article = Rs.50

Therefore, SP of an article = \( \Large \frac{50 \times \left(100-20\right) }{100} \)

=\( \Large \frac{50 \times 80}{100} \)

Hence, cost price of an article = \( \Large \frac{40 \times 100}{ \left(100+25\right) } \)

= \( \Large \frac{40 \times 100}{125} \) = Rs.32