Why teach mental computation?

Mental computation is now recognised as an important form of computation. The importance can be summarised as follows:

• it is the most common form of computation used by adults.
  ("85% of calculations done by adults in their daily life." McIntosh and Northcote 1998)
• it is used for estimation
• it is needed to check calculator answers
• students see it as an easy way of doing calculations
• it is an excellent way of learning how numbers work
• it is a creative and problem solving approach to number.