After the increase in the price of tea by 20%, Teena is able to buy 3.5 kg less for Rs. 420. Find the original and increased price of the tea per kg.     

Let the original price (O.P.) be Rs. x  per kg.  New price (N.P.) = 120% of x  = Rs.  6x/5 per kg. Quantity of tea the Teena could buy at original price =  420/x kg. Quantity of tea she can buy at new price =  (420 × 5)/6x  = 350/x kg Given that difference between the quantity at original price and at new price is 3.5 kg. 420/x - 350/x = 3.5  ⇒  x  = 20 Original Price = Rs.20 and New Price = Rs. 24  Alternate Method: New price = 420 20%/3.5 =84/3.5  =  84/(7/2) = 12 2 = Rs. 24/Kg let old price = x old price: new price = 100 : 120 = 5 : 6 = x :24 so x  =20  Rs/Kg