At the moment Boots have reduced all of their Xmas stock by 50%. It's called a half price sale and to help all the customers they have put up notices explaining how to convert the old price to the new price eg £1 becomes 50P and £2 becomes £1 etc.
I'm probably showing my age but when I went to primary school (early 1950's)we were taught mental arithmetic. Nowadays the schools allow the pupils to use calculators and computers to do even the simplest of calculations.
I remember helping with some tests of new recruits to the company I worked for and one of the questions was "what is 50% of 100". The answers ranged from one half to 5,000. Only two of the twenty people tested got it right.