I spend too much time reminding my students that the currencies they work with (pounds, euros, dollars etc.) must be written to two decimal places or the nearest whole number (depending on whether the major or minor unit is being used) with the correct unit.  It is incredibly common for students to just write a pound sign in front of their unrounded answer, particularly when they are using a calculator and the display shows 3.5 (or worse 7/2).

I have started to collect examples to try to explain why some struggle with what I consider to be a relatively easy concept.

• In trips to the market, or anywhere else with handwritten price labels, it is common to see items priced with a combination of units e.g. £2.10 p, or no units at all e.g. 1.95
• It is becoming increasingly common in some cities such as London to see the price of items on pub and restaurant menus written predominantly to one decimal place, for example ‘Ice cream: £4.5’
• At petrol stations prices are often quoted to the nearest tenth of a penny, 105.9 p per litre or £1.059 per litre.
• Exchange rates are regularly given to four decimal places e.g. €2910 for £1.
• Not all currencies across the world have two decimal places. Some have zero decimal places (e.g. Japanese yen), some have three decimal places (the dinar in many countries), and in Madagascar the minor unit is one fifth of the major unit so currency would be written to one decimal place.

I would love to add to this collection, please post any more that you or your students are aware of.

All the best,

Debbie Barton

Debbie Barton is a teacher, examiner and maths consultant with over 20 years’ experience. She’s written a number of books including Complete Mathematics for Cambridge Secondary 1. She also worked as a Gifted and Talented trainer and is passionate about ensuring able students are challenged with exciting stimulus.