After increase in the price of coffee by 15%, a person is able to buy 3 kg less for Rs. 1,840. Find the original and increased price of the coffee per kg?

Let the original price (O.P.) be Rs. x per kg.

New price (N.P.) = 115% of x = Rs. 23x/20 per kg.

Quantity of coffee the person could buy at original price = 1840/ x kg.

Quantity of coffee he can buy at new price = 1840 × 20/ (23x) = 1600/x kg

Given that difference between the quantity at original price and at new price is 3 kg.

1840/ x - 1600/ x = 3 ⇒   240/ x = 3 ⇒ x = 80

O.P. = Rs.80 and N.P. = Rs. 23x/ 20 = 23 × 80/20 = Rs.92

Alternate method:

Increase price = RS × change in price change in quanity = (1840×15%)/ 3 = 92

Now original price : increased price  = 100 : 115 = x : 92

So x  = 100×92/115 = Rs 80

So original price = Rs 80 & increased price = Rs. 92