It’s a sunny Saturday ((at the time of writing. I don’t know when you’re reading this)), and two maths items have caught my eye.

Firstly, a bit of a cock-up on the sums front from Andover Tesco (via [twit handle=”reeveshall”]):

Eight grand for a kilo of blueberries? That can’t be right. It’s hard to figure out what they’ve done wrong here - a kilogram is only eight of their 125g servings, so the correct price is £8 per kilo. My first thought was “maybe they’ve confused grams and kilos?” - but the blueberries are about 0.8p per gram, not £8,000. ((On later thought: perhaps the weight was put in as 0.125g instead of 125g. That would explain it.))

The other story was even more amusing: the Spanish Navy has built a submarine that’s 70 tonnes heavier than it ought to be, because someone missed a decimal point early in the design stages ((An error in their floating point arithmetic, as [twit handle =”realityminus3”] says.)). Oops. It’s going to cost them somewhere in the region of ten million quid to put right. (They could, of course, use that money to buy buoyant blueberries.)

Back to Tesco, though; they responded, good-naturedly:

…and for a moment I was reassured. But then I thought, no: the problem wasn’t with the calculator. It’s with no-one thinking “8,000 punnets of these blueberries might come out to a bit more than a kilogram.” It’s with no-one saying “that number looks odd.” And it’s with everyone saying “It came out of the computer, so it must be right.”

That’s the kind of thinking that can cost you millions of pounds.