A showroom advertises: 'Buy one shirt at the marked price of ₹1200 and get a second shirt at 40% off.' A customer who buys two shirts gets an effective discount of what percent on the two shirts together?

Two shirts are worth $2\times 1200$ = ₹2400, and the customer pays 1200 + 720 = ₹1920. The discount is ₹480 on ₹2400 = 20%. (The advertised 40% applies to one shirt only; spread across both shirts it is halved. A true 'buy one, get one free' offer would work out to 50% by the same reasoning.)