It’s the arithmetical trick that’s been causing delight and surprise but you’d better try it out on friends soon – because the later it gets into the year, the less likely it is to work.
Currently doing the rounds on social media, the poser involves a series of simple questions.
First ask your friend to think of their shoe size, then – using a calculator or a pen and paper – they should multiply it by five.
Next they add 50, and then take that total and multiply it by 20. They should add 1,015, and finally subtract the year of their birth.
Magically, the result should be their shoe size and age, together making up a three or four-digit number. The trick works regardless of whether you use UK, European or American shoe measurements.
However, it won’t work for someone who has already had their birthday this year, or who is more than 100 years old.
Carol Vorderman – the former Countdown maths whizz – welcomed the popularity of the trick.
She said: ‘I love this great little game. It’s simple algebra. It’s incredibly valuable because it takes GCSE maths and turns it into something fun.’
The TV presenter added that at the start of next year, the trick will only work if you add 1,016.
The best way of explaining it is by looking at how it reached the shoe size and the age separately. The formula is able to work out someone’s age because it subtracts their year of birth from the number 2,015.
The way it creates 2,015 is the step which adds 1,015 to 50 multiplied by 20, or in other words, 1,015 plus 1,000. Your shoe size is correctly identified because the step that multiplies it by five, and then by 20, simply adds two zeroes on to the end of the original shoe size. For example if your shoe size is 11, it will work out as 1,100. The final step of the equation adds that number to your age so the first two numbers are your shoe size.
Cambridge professor David Spiegelhalter said: ‘I hope it inspires people to think, “Why does this work” and actually work through the problem. Any child who does that will learn a huge amount.’
Here’s a simple maths trick your can impress your friends and family with, writes The Telegraph.
The ‘magical’ maths trick which shows how you can determine a person’s age from their shoe size has been widely shared on social media in recent weeks.
This is how it works:
1. Take your shoe size
2. Multiply it by 5
3. Add 50
4. Multiply by 20
5. Add 1015
6. Subtract the year you were born
The answer you come up with should be your shoe size (first two digits) and your age.
The one caveat is the trick will not work if you’ve already had your birthday this year.
So how does it work? You can see how the trick works using some basic algebra:
Real Clear Science’s Alex B. Berezow explains: “Do you see why it works? No matter what your shoe size is, it will always be the first two digits of the answer.
“The age part should be obvious. [The current year] – y [your birth year] will give your age.”
This article originally appeared dailymail.co.uk