Maths question - Civil Service is wrong (we now have 100% more threads about the subject)

[Sharingaroomtinightthen]

When I posted late last night I thought I’d get maybe half a dozen replies confirming the question didn’t have the correct answer and advising whether to tell the Civil Service recruiters. But here we are 1000 posts later.

https://www.mumsnet.com/talk/am_i_being_unreasonable/5384347-maths-test-to-think-civil-service-have-it-wrong

The insisting they are right might be due to neurodiversity. As someone with a lot of experience in that field I recognise that particular stubbornness and even the phrasing of it.

🤔.

Oh I see. Yes, I guess you're right. I think there are a few reasons why people are getting the wrong answer.

And as @SoSoLong says below, even when explained, some purportedly skilled mathematicians have doggedly maintained it's ambiguous or one of the incorrect answers. I find that incomprehensible.

@Samscaff 125 is what I originally thought. Then I had 225. My dad, who is much more expert in such a field, agrees with @SerendipityJane and says 450 😂 which is at least one of the answers on there

so… I shall eagerly await if OP gets a response!

Afraid your dad is wrong! Feel free to show him my earlier explanation and challenge him to find an error in it…

For some reason I am reminded of a wonderful phrase from "Avenue 5", uttered by the impossibly perfect Hugh Laurie ...

"We've just seen 7 people stupid themselves to death".

The Monty Hall problem is a beautiful example of how probabilities can be counterintuitive.

This is an example of a poorly worded question - poorly worded because, while the question is unambiguous, the correct answer is not provided so we can't be sure that the setter understood the words they were using, like so many on this thread.

Not remotely the same thing.

I am firmly in the 125% camp, however I think I have just spotted a flaw:

The question says, "In one year the circulation of News Today doubled." But this year can't be "the first year" of circulation, otherwise you're doubling zero.

So it can be the first year that we're looking at, but not the first year of circulation. So when we're asked to compare the end of the first year with the end of the third year, it's not truly the first year.

However, doubling, tripling or reducing zero by a quarter all give you zero, so I'm sure that's not what the question-setter intended.

Hope that makes sense.

Oh I spent quite a while today thinking exactly that!

The question says, "In one year the circulation of News Today doubled." But this year can't be "the first year" of circulation, otherwise you're doubling zero.

It never claimed to be the first year of circulation though.

It doesn't say that we are starting at zero.

It could be looking at a normal newspaper that has been around for many years.
Then in 1 year, the circulation doubled. etc

Well the actual question posed is, "What was the percentage increase in circulation of News Today from the end of the first year to the end of the third?"

So it kinda does, or at least could justifiably be interpreted that way imo.

I know it doesn't state explicitly that we are starting at zero. But if it's the first year of circulation [of a newspaper] then it's implicit that we are starting at zero as if it was already being circulated it wouldn't be the first year of circulation.

The "first year" of anything implies nothing has gone before it (although I suppose the year 1AD would be an exception...).

Not just me, then! (Not that that means a lot on this thread...)

To be clear, I'm not suggesting that's what the question means as it wouldn't make sense, but there is a potential ambiguity there.

Ah, but a new newspaper doesn't start with 0 copies, on the first day they've got to put some out.

Where does it say that ?

To be fair, it doesn't, just my logic that the first day of a newspaper in circulation is when they put some copies out on the street.

That would be the first day of Year 1 though, wouldn't it?

Yeah, so they launch on the first day of year 1 with 10k, by the end of the year they reach 20k.

As with the Monty Hall Problem, there is a simple, correct answer that people, including experts, get wrong. This is independent from the missing answer in the button list, which is a separate conundrum. If the question itself is unambiguous yet so many mathematicians earnestly explain why it's 225% or somesuch, how is that not a viridical paradox?

Ah yes, that works.

I love the Monty Hall problem

Imagine there are a million doors. I know the door that the prize is behind.
You pick a door.
I then open the doors - and every time I open a door, there is no prize behind. So after opening all the other doors, we are left with 2 doors.

The door you picked at the start.
Or the other door that I haven't opened yet

There are also 999.998 other open doors with no prize behind. Just lots of goats.

Do you swap doors - or do you stick with your first choice?

Or does it make no difference?

I don't think that has anything to do with this question - which is straightforward and unambiguous. I think it's because many advanced mathematicians aren't actually that good at simple maths. I got stuck behind one of my maths professors at a uni shop one day - the guy had all sorts of awards for problems he'd solved but he couldn't work out how much he needed to pay or confirm the change.

Switch! Switch! The other door has gone from 1/1000000 to 999999/1000000, while yours is still at 1/1000000!