The marked price of an article is increased by 25% and the selling price is increased by 16.66%, then the amount of profit doubles. If the original marked price be Rs. 400 which is greater than the corresponding cost price by 33.33%, what is the increased selling price?

As given in the question, Marked price is 25% more than the Cost price.

=> C.P of the article =  $\frac{3}{4} x 400 = 300$

Now, 

Let the original S.P of the article be Rs. P

Now the new S.P = P +  $\frac{16.666 +13.333}{300} x P$

=> S.P =  $\frac{7P}{6}$

According to the question,

$\frac{7P}{6} - 300 = 2P - 300$

=> 5P = 1800

=> P = Rs. 360

Hence, the increased S.P = 360 x 7/6 = Rs. 420.