On a TV Quiz, I have just watched a woman who claims to teach remedial classes to young adults and teenagers answer the following question:

“A man pays 500 pounds for a car. Its price has been reduced by 60%, what was the original price?”

She started by trying to work out 60% of 500, before realising her mistake – that the 500 pounds was 60% of the figure she needed to find. However, each time she tried to solve it by using 50% instead of 60%, then adding 10%. Her answer to the question was 1100 pounds.

The same woman answered

“What organ of the body is involved with exchanges of gases”

With “It can’t be lungs, as that is air, not gases”. Having gone around in circles, and briefly considered farts, she answered “Lungs”, but still no wiser.

Won’t someone think of the children?

Er, if the figure is 500 pounds after having been reduced

by60% then the original cost was 1250 (500 is 40% (100% – 60%) of the original). Which is a lot simpler than trying to divide by 60% (833.33 recurring).However, I always wonder with those shows how well I’d do if I were put on the spot. I think that most people tend to freeze in that situation, and five minutes after the quiz they are cursing themselves for stupid answers (I had that in my finals, I’d already answered a question which showed that I knew the term (I’d used it to get the answer), but when another question said “what does that term mean?” I went totally blank).

“then the original cost was 1250”

You know that, and I know that (and all the kids knew that too – this was ‘Are you smarter than a 10 year old’). Unfortunately, the woman had already used all 3 opportunities for the kids to help her, on earlier questions (and she only answered 6 questions in all).

Regarding blanking – yes I know it can happen, but it is usually fact based (or – in my case – lyrics). This was schoolboy maths, with someone who had said 10 seconds before that she teaches maths. Not only did she fail to answer correctly, but she tried to use a method that couldn’t do anything but fail.

One of the items I wanted at Halsway was mis-priced – marked at £400 instead of £4 – so she offered it at 100% discount, ie £4

What subjects did she claim to teach?

Maths was one of them!

But in fact my original calculation was indeed 833 (etc.), because like most people I mixed up “is now 60%” and “reduced by 60%”. I’m not sure that I wouldn’t also have tried multiplying by 60% if I hadn’t read it first. Teaching it to someone, with your book there with the correct answer (and probably having studied it before the lesson) is not the same as doing it on the spot.

Heck, I remember a head of maths department, with two degrees from Oxford, managing to do 1+2+3=4 in front of a class of double maths A level students, none of whom noticed either! Admittedly it was while reducing simultaneous differential equations, but he basically wrote down a column of coefficients as 1, 2, and 3 and then wrote 4 as the sum. It wasn’t noticed until a lot later when the equation wasn’t solving, one student had written it down and looked back at the working.

Yes, but as I said, she didn’t even multiply it by 60% in an error of miscomprehending the question. In both her calculations she calculated by using 50%, then doing 10% on top of that.

No matter whether you read a question right or not, or can do a sum in front of a TV studio audience, anyone who teaches maths should know that you can’t get to 60% by doing 50% first, then 10%. That’s how she reached 1100 – “If it was a 50% discount, then 500 pounds was originally 1000 pounds, but it was 60%, so I need to add on 10% more.” It don’t work that way!