Question

a man sold 20 articles for Rs. 60 and gained 20%. how many articles did he buy for Rs 60?

Answer 1

Let buying price=BP 
Selling price Rs60= buying price for 20 articles+ gain 
 told gain is 20%
which means gain=(BP)X (20/100) = 0.2 BP
that shows selling price =60= BP + 0.2BP
 Which means 60=1.2 BP
from which we gets BP= Rs50.  
He got 20 articles for Rs 50  or (20/50)  article per  each Rs.
 So for Rs60 he will get (2/5) X 60 which is  24

Answer 2

20 articles cost price = 60×100÷120=50
rs 50 of cost price of 20 articles
so that rs 1 cost of =20/50
so rs 60 cost of article= 20×60÷50=24 ans ok