Passage: Building on its success, Airbus launched the A320, particularly notable for being the first commercial jet to use a fly-by-wire control system. The A320 has been, and continues to be, a great commercial success. The A318 and A319 are shorter derivatives with some of the latter under construction for the corporate business jet market as Airbus Corporate Jets. A stretched version is known as the A321. The A320 family's primary competitor is the Boeing 737 family.The longer-range widebody products— the twin-jet A330 and the four-engine A340— have efficient wings, enhanced by winglets. The Airbus A340-500 has an operating range of 16,700 kilometres (9,000 nmi), the second longest range of any commercial jet after the Boeing 777-200LR (range of 17,446 km or 9,420 nautical miles).All Airbus aircraft developed since then have cockpit systems similar to the A320, making it easier to train crew. Production of the four-engine A340 was ended in 2011 due to lack of sales compared to its twin-engine counterparts, such as the Boeing 777.Airbus is studying a replacement for the A320 series, tentatively dubbed NSR, for "New Short-Range aircraft". Those studies indicated a maximum fuel efficiency gain of 9–10% for the NSR. Airbus however opted to enhance the existing A320 design using new winglets and working on aerodynamical improvements. This "A320 Enhanced" should have a fuel efficiency improvement of around 4–5%, shifting the launch of an A320 replacement to 2017–2018.

Question: How much improve fuel efficiency should the A320 Enhanced have?
4–5%