# The Guardian and numbers

Sainsbury’s Like Tesco, Sainsbury’s also offers a main, snack and a drink for £3, but the discerning shopper can get better value. A New Yorker sandwich (£2.80), along with a bottle of flavoured water (£1.40) and a slice of carrot cake (£1), adds up to £5.20. The £2.20 meal-deal saving – or 73% – is a substantial reduction on buying the items individually.

Eh?

73%?

It’s obvious what they’ve done, calculated the saving against the price paid, not he saving against the original price.

But if Sainsbury’s actually advertised that as a 73% savings then they’d be trying to put someone in jail for having done so.

Think through it for a moment. If something is £10 normally and I offer it for £5 in a sale, am I allowed to advertise a 50% saving or a 100% saving?

The Guardian and numbers, eh?

The Co-operative The Co-op’s deal across its 2,800 stores follows the same lines as its rivals, with a main, snack and drink for £3.25. A deep-fill egg and bacon sandwich (£2.75), a 475ml can of Red Bull (£2.39), and a chicken satay snack with dip (£1.19) come in at £6.33 when priced individually. Under the meal deal this gives a saving of £3.08 – almost the same price as the deal itself.

Would that be a near 50% saving or a near 100% one?

## 17 thoughts on “The Guardian and numbers”

“Sainsbury’s Like Tesco, Sainsbury’s also offers a main, snack and a drink for £3, but the discerning shopper can get better value. A New Yorker sandwich (£2.80), along with a bottle of flavoured water (£1.40) and a slice of carrot cake (£1), adds up to £5.20.”
So £5.20 is better than £3? Ahhh no, but I had to read that a few times before I understood what they meant.

2. Should have said you pay 73% more if you buy them individually if they wanted to use the bigger number.

I get a similar problem with Chinese lab staff applying % corrections to test results from known machine errors all the time. The main problem is that the damn manufacturer made the same mistake when instructing in the manual. i.e instructing to calculate the correction using the error % of the true value not the measured one.

3. You’d be amazed how many French engineers don’t understand percentages. At least the ones I work with.

4. Ahh, the %age is clearly an evil tool of the neoliberal sophist. Whodathunkit?

5. Just think, if the combined price of the individual items had been £6 then buying the meal deal would give a 100% saving. And you just can’t do better than that can you.

6. The fact that you can discount something that’s usually \$10 to \$5 proves you are an evil profiteering neoliberal sophist. You should sell everything precisely at cost. The fact that supermarkets charge on average 5 times factory gate prices for stuff proves they are making 400% profits. Am I getting close?

7. My investment provider (who shall remain unnamed) told me that an increase in my investments from £9,000 to £10,000 represents a 10% gain. This is financial services company not getting their sums right. I’ve tried telling them. Perhaps I should open a Twitter account just to shame them.

8. Actually, Sainsbury IS better value, because their sandwiches are nicer than Tesco’s offerings.

9. Surprising how many people don’t realise that you “only” need a 50% discount to cancel out a 100% mark-up.. 🙂

10. “Actually, Sainsbury IS better value, because their sandwiches are nicer than Tesco’s offerings.”

The best value is making your own. A ham sandwich (with good deli ham) is about 60p of materials. A supermarket one (with cheap ham) is £1.10.

11. Percentages are incredibly basic arithmetic (not, repeat not ‘maths’), of the sort that I learnt at prep school aged perhaps 10. If you are a grown adult and cannot work out the percentage saving on something being reduced from £5.20 to £3 (42.3%) then there is a fairly large cognitive deficit lurking somewhere, one that would on the face of it militate against your being paid to write things about money. Being a Grauniad journo pretty much guarantees that you’re not very good at sums, but being this bad is worrisome.

I wonder what is the most advanced mathematics commenters here use on any sort of a regular basis professionally. I think for me the most recent was finding a set of primitive roots modulo a smallish prime for a hashing algorithm and doing a bit of vector algebra to draw arbitrary ellipses in Google Earth, both of which were fairly trivial. It’s a bit odd how little I use of the advanced stuff I learnt given that I work in a nominally technical discipline.

12. I wonder what is the most advanced mathematics commenters here use on any sort of a regular basis professionally.

Bayesian probability stuff. But then I work now in what is much more art than science. When I was doing proper engineering, it was all arithmetic. Despite the endless years of math at uni.

13. “Regular basis”: small sets of nonlinear ODEs, both IV and BV problems; large sets of nonlinear transcendental equations, where the number of equations in the set depends on the answer (honestly!), and we came up with a beautiful algorithm using nested continuation methods.

Occasional: integral equations, finite element methods, tensor algebra, spherical trig, bits and bobs of stats. I once proved a nice little set of theorems using nothing more advanced than Laplace Transforms; ooh it was a joy.

Most memorable advice I got from a mathematician when I was young: “Your problem isn’t interesting, it’s merely very difficult.”

I think a lot of this was made possible, in part, by my having had a very good maths teacher at school. That was before the Forces of Progress decided to bugger up the schools, the fucking philistines.

14. If you can “give 110% effort”, you should clearly be able to get a 110% saving. Or is the lack of those another spike hammered in to the caring society by those evil neo-liberal banksters?

15. Of course, this disregards the value of each competitor’s offering. Personally, I’d rather optimise for value rather than discount from RRP.

But then, some people optimise for the value of state benefits they can receive, rather the quality of life their total income – both earned or unearned – affords them.