Buy three shirts and get one free'

‘Buy three shirts and get one free’ is an example of one of the techniques of sales promotion. Identify and explain the technique.

It is an example of quantity gift. In order to clear off excess inventory, company generally offers extra quantity of the product to enhance the sale or to clear the stock e.g. a shaving cream offers ‘40% Extra’ or a marketer of shirt offers ‘Buy three get one free’.