# The Super Subtraction Feat

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### How I Unofficially Broke The World Record That Never Was

One of the 70-digit subtraction sums I did for training purposes.

In April, a gentleman called B. Sai Kiran became, briefly, internet-famous for doing arithmetic. In Hyderabad, he subtracted a 70-digit number from another in the barest smidgen over a minute – 60.05 seconds, at the second attempt.

Very good, I thought – as did everyone else; a triumph, as Mr Kiran said, for Vedic Maths. But there was something bugging me. Finally, I realised what it was:

The attempt being for a Guinness World Record, it was ensured that all digits except the first in the minuend are smaller than the corresponding digits in the subtrahend, thereby raising the complexity level of the calculation.

This sentence is a mini-masterpiece of misdirection. I skipped over it at first, put off by the unfamiliar words minuend (the first number) and subtrahend (the second), and assuming that anyone who uses big words must know what they’re talking about. Even when I thought about it in more detail, it seemed to make sense – doing it the traditional way, if all of the numbers in the second number are smaller, you have to borrow one from the number to the left each time.

### There’s a big but, though. An awfully big but.

If you know that every number on the lower line is bigger than the one above, the enormous sum simply turns into a memory trick. If, somewhere in the middle of the sum, you have a 3 above an 8, you know for sure that you’ll have borrowed 10 from the left and lent one to the right, turning it into 12 – 8 = 4. Whenever you see a 3 above an 8 (or any pair with a difference of 5), you can immediately write down 4 as the answer.

Suddenly, 60 seconds to do a huge sum didn’t seem like such a big ask. Surely, anyone who can memorise the times tables should be able to commit the 45 number pairs to memory and churn them out on demand?

But who?

I needed someone with a pretty good memory. Someone who would take personal offence at the idea of a piece of misdirection being used to justify a world record and media coverage. Someone who could write a program to generate 140-digit sums with the necessary properties. Someone who would devote his life to preparing for a pointless challenge.

### With a sigh, I realised I was playing my tune…

The montage, at this point, would show me mainly battling with a printer (it’s surprisingly hard to convince my computer to fit 70 digits on one line), sharpening pencils (eventually I went mechanical), and figuring out the stopwatch feature on my phone. Finally, I was ready to make an attempt on the record, in private.

You know? It’s harder than it looks, regurgitating digits at speed. My first attempt barely broke the two minute mark. Changing direction – as Mr Kiran does – so as to work from left to right made a slight improvement.

There was only one thing for it: I’d have to practise. It turns out, if you practise something over and over, with immediate feedback, you get better and quicker at it. Who knew?

I made flash cards. I spent the time between classes improving my handwriting. I stopped crossing my sevens, briefly, but realised I was concentrating so hard on that that it was slowing me down.

My times… stagnated around the 90 second mark for a few days. One day I woke up and I was suddenly stuck at 84, without consciously changing anything. This was the pattern throughout: plateau for a few days, keep at it, and one day find things were suddenly better. None of your nice, neat linear progression stuff here; just ugly quantum leaps in performance.

And then, just in time for May’s East Dorset Mathsjam, I broke through the one-minute mark. Not every time, but once in a while – often enough to give me hope that I could do it in front of an audience. I came up with a protocol for an unofficial world record attempt. I drove to Wimborne. I waited for a lull in conversation. I nearly missed my chance, so I finally interrupted Ben’s fascinating magic trick and said ‘I brought something.’

Reader, I smashed the record.

My first attempt, in front of four witnesses, was clocked at 52 seconds – by far my personal best, before or since.

### Getting Guinness World Records Involved

You can’t – according to my friends – smash a world record unofficially and leave it at that. You have to apply to Guinness World Records – exactly the kind of admin burden that is one of the reasons I’m not a teacher.

But, well. I applied. It takes ages, unless you pay for the fast track – and while I’m willing to spend dozens of hours training to shave a few seconds off of the time it takes me to do an oddly specific bit of arithmetic, the idea of sending someone a few quid to shave a week or two off of a response time grates.

In honesty, I’d forgotten about it until Wednesday, when GWR got back to me and suggested I attempt their ‘most calculations in one minute’ record.

Nooooooo! That’s not the one I trained for. And besides, my personal beef is with this Kiran guy in Hyderabad, not some snotty kid in China. I replied (in politer terms) that I was particularly interested in the Super Subtraction Feat, bringing in @gwrnews on twitter (A* for the twitter team, by the way – responsive and friendly).

According to GWR, B. Sai Kiran’s record… is no such thing. Their email states “The record that [you] refer to is not an official Guinness World Record.”

How disappointing! It’s not clear who – apart from me – was hoodwinked. The Hindu article clearly states that Mr Kiran set the Guinness record, although the article says the record was awarded by Record Holders Republic and only submitted to Guinness – the kind of detail a hurried sub-editor could easily miss.

So… all of my training – and hopes for a small human interest article in the local press – are dashed. All that work – for nothing. Not even a certificate at the end of it!

Ah well, I’m going to console myself the only way I know how, by eating. Know what I fancy? A giant take-away.

## About the author

• #### Colin Beveridge

Colin Beveridge is the author of The Maths Behind and several other popular maths books. Based in Weymouth, Dorset, he divides his time between looking after his children and writing about maths.

### 4 Responses to “The Super Subtraction Feat”

1. Dave Gale

Wow how cool is that? You’re certainly a record breaker in my eyes.
Anyway. Did you look into whether you might be able to break a real guiness world record?
And.
How is it that newspapers can get away with printing things that are simply not true? It does annoy me!

Congratulations on your feat but I won’t be challenging it ;-)
Dave
@reflectivemaths