Aman buys a book for $20 and wishes to sell it. what price should he mark on it if he wishes for a 40% discount and 50% profit on the cost price. explain your answer!

With that particular larcenous scheme in mind, he will price the book
regulaly at $50 .   See the price-tag in the attached picture.

With a regular price of  $50  written all over it, he can run a spectacular,
once-in-a-blue-moon, "40%-off" sale.

   40% of $50  =  0.4 x $50  =  $20 off

   $20  off of  $50  ===>  Sale price  =  $30 is what the buyer will pay
during the spectacular sale.

Then, the sale price of  $30  is  (30/20) = 1.50 of his own original cost.

1.50 of his own cost means  0.50  =  50%  more than he paid for it.