Three people enjoy a meal at a Thai restaurant. The waiter brings the bill for £30 so each person pays £10.
Later the chef realises that the bill should have only been £25 so he sends the waiter back to the table with £5. The waiter was not very good at Maths and could not figure out how to divide the £5 so he gave each person a £1 and kept £2 for himself.
So....the three people have paid £9 each for the meal.
3 x £9 = £27
The waiter kept £2
£27 + £2 = £29
What happened to the other pound? Does this make sense?
This activity is suitable for students of mathematics all around the world. Use the button below to change the currency symbol used to make it more relevant to your students. You may wish to choose an unfamiliar currency to extend your students' experience.
How did you use this starter? Can you suggest
how teachers could present or develop this resource? Do you have any comments? It is always useful to receive
feedback and helps make this free resource even more useful for Maths teachers anywhere in the world.
Click here to enter your comments.
If you don't have the time to provide feedback we'd really appreciate it if you could give this page a score! We are constantly improving and adding to these starters so it would be really helpful to know which ones are most useful. Simply click on a button below:
This starter has scored a mean of 3.6 out of 5 based on 264 votes.
Danny Baker on his wonderful BBC radio 5 live programme suggests a unique solution to the missing pound puzzle.
The final paragraph of the story should read:
The waiter kept £2
£27 − £2 = £25, the correct cost of the meal.
Here is a similar puzzle from Thailand: "You borrow money from your Dad (500 baht) and your Mom (500 baht) to buy a phone that costs 970 baht. You then you have 30 baht change from the shop so you return 10 baht to Dad and 10 baht to Mom and you keep 10 baht yourself. But 490 + 490 = 980 and the 10 baht that you keep totals 990 baht. Where is the missing 10 baht?"
Your access to the majority of the Transum resources continues to be free but you can help support the continued growth of the website by doing your Amazon shopping using the links on this page. Below is an Amazon search box and some items chosen and recommended by Transum Mathematics to get you started.
You are buying a (driverless) car. One vehicle is programmed to save as many lives as possible in a collision. Another promises to prioritize the lives of its passengers. Which do you choose?
Welcome to the age of the algorithm, the story of a not-too-distant future where machines rule supreme, making important decisions – in healthcare, transport, finance, security, what we watch, where we go even who we send to prison. So how much should we rely on them? What kind of future do we want?
Hannah Fry takes us on a tour of the good, the bad and the downright ugly of the algorithms that surround us. In Hello World she lifts the lid on their inner workings, demonstrates their power, exposes their limitations, and examines whether they really are an improvement on the humans they are replacing. more...
Teacher, do your students have
access to computers?
Here a concise URL for a version of this page without the comments.
Here is the URL which will take them to a related student activity.
A man had an apple stall and he sold his larger apples at 3 for a pound and his smaller apples at 5 for a pound.
When he had just 30 apples of each size left to sell, he asked his son to look after the stall while he had lunch. When he came back from lunch the apples were all gone and the son gave his father £15.
The father questioned his son. "You should have received £10 for the large apples and £6 for the 30 small apples, making £16 in all."
The son looked surprised. "I sold them all at the average price of 2 small and 2 large for £1. Four into 60 goes 15 times so I am sure £15 is correct.
Where is the missing pound?
This extension is adapted from a puzzle in Amazing Brain Teasers by Erwin Brecher
The average cost of the large apples is £1 ÷ 3 = 33⅓p.
The average cost of the small apples is £1 ÷ 5 = 20p.
So the 2 small and 2 large apples should have been sold for
33⅓p + 33⅓p + 20p + 20p = £1.06⅔
to earn the £16