3 Packs of cigarettes retail for 15.87. There is a special buy 2 get one free. How much will the customer save?

3 = 15.87

therefore 1 = 15.87/3 = 5.29

if 1 packet = 5.29 then 2 packets will cost 2 * 5.29 = 10.58

If the offer is 2 for the price of 2 then the saving will be 15.87-10.58 = 5.29 (the cost of one packet).