By selling 50 articles for Rs. 35, a man loses 30%. How many should he sell for Rs. 25 to gain 25% in the transaction?

Let the CP of each article = Re. x,

So, CP of 50 articles = Rs. 50*x = Rs. 50x

Now, SP of 50 articles = Rs. 35 and loss % = 30%,

[50x(100 – 30)]/100 = 35

50x*70 = 35*100,

x = 1,

So, CP of each article is Re. 1,

Now, let the number of articles sold in Rs. 25 be y 

So, CP of y articles = y*1 = y,

Now, SP of y article = 25,

y(100 + 25)/100 = 25,

y*125 = 25*100,

y = (25*100)/125,

y = 20,

So, number of articles is 20.