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If there are five points on the surface of a sphere, then no matter how they are arranged at least four of them lie in the same hemisphere.
Proof: Pick any two of the points. These two points, taken with the centre of the sphere, define a plane that cuts the sphere into two hemispheres, both containing the points we picked.
Three points remain, and of these at least two must lie in the same hemisphere, which will then contain the required four points.
If there are five points on the surface of a sphere, then no matter how they are arranged at least four of them lie in the same hemisphere.
Proof: Pick any two of the points. These two points, taken with the centre of the sphere, define a plane that cuts the sphere into two hemispheres, both containing the points we picked.
Three points remain, and of these at least two must lie in the same hemisphere, which will then contain the required four points.
"Thank you so much for the lovely sofa and matching armchairs", said Tom sweetly.
Suppose we mark five points of the surface of a sphere.
Can you prove that however the points are distributed it is always possible to draw a hemisphere that include at least four of the five points in its interior or on its boundary?
This puzzle appears in many places and was included in a maths competition as recently as the early 2000s. but I think it must go back further and may have first been published by Martin Gardner, although I don't have the reference.
Can you prove that however the points are distributed it is always possible to draw a hemisphere that include at least four of the five points in its interior or on its boundary?
This puzzle appears in many places and was included in a maths competition as recently as the early 2000s. but I think it must go back further and may have first been published by Martin Gardner, although I don't have the reference.
Do you like my grammar hardback red new fat big lovely book?

Most native speakers of English will instinctively agree the order of the adjectives in my sentence above is wrong—weird even—without necessarily being able to describe exactly why; it flouts some rules that we all know but are not normally conscious of. These rules are difficult to write down precisely but roughly speaking follow a sort of semantic spectrum. The Cambridge Dictionary gives this order
opinion - size - physical nature - shape - age - colour - origin - material - type - purpose
If we rewrite my initial sentence using this order we get
which sounds perfectly normal, albeit a bit wordy perhaps.
Mu new dictionary—the one pictured—calls the rules "Adjectival order", although "Royal Order of Adjectives" is a more colourful name.

Most native speakers of English will instinctively agree the order of the adjectives in my sentence above is wrong—weird even—without necessarily being able to describe exactly why; it flouts some rules that we all know but are not normally conscious of. These rules are difficult to write down precisely but roughly speaking follow a sort of semantic spectrum. The Cambridge Dictionary gives this order
opinion - size - physical nature - shape - age - colour - origin - material - type - purpose
If we rewrite my initial sentence using this order we get
my lovely big fat new red hardback grammar book
which sounds perfectly normal, albeit a bit wordy perhaps.
Mu new dictionary—the one pictured—calls the rules "Adjectival order", although "Royal Order of Adjectives" is a more colourful name.
Eating my coleslaw on Monday, I wondered about the etymology. The first element is recognisable as meaning "cabbage", as in kale, Old English cole, German kohl, and Italian Cavalo, etc. all stemming (pun intended) from Latin Caulus, stalk or cabbage.
But "slaw" seemed a bit mysterious.
It turns out to be from Dutch, sla, slaw, a contraction of "salad", and we borrowed "coleslaw" directly from Dutch koolsla,"cabbage salad".
But "slaw" seemed a bit mysterious.
It turns out to be from Dutch, sla, slaw, a contraction of "salad", and we borrowed "coleslaw" directly from Dutch koolsla,"cabbage salad".
punctual: I’ll fight everyone
See here for the problem I posed.
The answer is the expected proportion of Heads and Tails is 50:50.
A plausible intuition is that the strategy described in the problem with result in more Heads being observed than Tails, but this intuition is misleading
Each coin flip is independent and over a large number of trials Heads and Tails will each turn up with about the same frequency, and no strategy we might decide to follow can change this ratio.
I wrote a Python program to simulate the problem and sure enough if we run it Heads and Tails each appear in with about the same frequency.
The answer is the expected proportion of Heads and Tails is 50:50.
A plausible intuition is that the strategy described in the problem with result in more Heads being observed than Tails, but this intuition is misleading
Each coin flip is independent and over a large number of trials Heads and Tails will each turn up with about the same frequency, and no strategy we might decide to follow can change this ratio.
I wrote a Python program to simulate the problem and sure enough if we run it Heads and Tails each appear in with about the same frequency.
import random
H = 0
for i in range(1000000):
throw = random.choice(['H','T'])
if throw != 'T':
H = H + 1
while throw != 'T':
throw = random.choice(['H','T'])
if throw != 'T':
H = H + 1
print('Heads per 1000000 Tails', H)
I was going to buy a cul-de-sac, but I decided it was a dead end.
Suppose 1,000 people take part in the following experiment.
Each participant is given a fair coin, which they proceed to flip one or more times, recording the outcome. As long as their coin turns up heads they keep flipping it. As soon as a tail comes up (but not before) they immediately stop flipping their coin.
What is the expected proportion of heads recorded versus the number of tails?
(This problem is usually framed a bit differently but I think the version given above is preferable to the traditional one.)
Each participant is given a fair coin, which they proceed to flip one or more times, recording the outcome. As long as their coin turns up heads they keep flipping it. As soon as a tail comes up (but not before) they immediately stop flipping their coin.
What is the expected proportion of heads recorded versus the number of tails?
(This problem is usually framed a bit differently but I think the version given above is preferable to the traditional one.)
We found this striking Turkey Tail fungus Trametes versicolor growing on a dead log in our garden.
From Wikipedia, it is found world-wide and lives by digesting lignin, a key structural component in plants= tissues. The fungus has been used in traditional Chinese medicine and a range of beneficial properties have also been claimed for it in the setting of conventional medicine. For a summary see this article. I haven't read enough to assess how strong the evidence is, and I think opinion is probably divided.
"I'm counting how many pots of tea you make", said Tom brutally.
This puzzle can be found in many places in the internet but was first published by Martin Gardner in his 'Mathematical Recreations' column in Scientific American. It goes like this (this wording is mine, not the original which I don't have to hand.)
Two mathematicians are sitting outside a café, and one say to the other, “I have three children, and the product of their ages is 36. Can you work out their ages?”
“No”, say the second mathematician, “I don’t have enough information”.
“Then what if I tell you the sum of their ages is equal to the number of that house directly opposite?” the first mathematician replies.
“Still not enough information”, answers the second.
“Well what if I tell you the oldest is called Bill?”, say the first.
“Aha, now I know the ages!” says the second mathematician.
1. Can YOU work out what the ages are? (Solution appears further down.)
2. Can you find a number different for 36 but which would still let the second mathematician deduce the ages if they knew the sum of the ages and the fact that the oldest child is called Bill?

PS The second triple is wrong see comments.
My crystal ball broke down so I took it back to the shop. They said they’d look into it.
A friend travelling in the Eastern Caribbean sent me some photos of flowers. This lovely plant is paperflower, or lesser bougainvillea, scientific name Bougainvillea glabra.
I'm disbelieving of this being a Harvard Interview Question, but that is the title given to a question circulating on social media. It runs as follows:
"7 men have 7 wives. Each man and each wife have 7 children. What's the total number of people?" |
---|
It's ambiguous and that's probably why it has gone viral, with people offering a variety of answers and opinions and even the occasional quip, such as "Were they going to St Ives?".
So it's not the maths that is interesting but the impetus to debate, discuss wrangle, argue. disagree and tut about the ambiguity.
Still, to get back to the boring old maths, I thought I would ask:
If 7 is replaced by n, what is the smallest answer that we could put forward a case for, and what is the largest?
If Musk got involved in a cover-up, would it be stretching things to call it Elongate?
Annie L. Pressland (1862-1933), from Wikimedia
A GPS is one that "leads you down the garden path". As you read it you think you are understanding it, then it socks you on the back of the head ("This makes no sense") but finally you realise you'd been reading it the wrong way and it makes sense after all. The canonical example is
"The old man the boat."
Another one, that is really hard to parse, is
"The complex houses married and single soldiers and their families."
Eh?#%~
The Wikipedia article says the first example "has been used to test the capabilities of artificial intelligence efforts" but that was in 2016, and today DeepSeek has no trouble, it's seen it before and can analyse it with no difficulty at all
I thought I would try making up my own GPS
Here's my attempt at a GPS sentence. It took me several goes before I was able to work the idea up into something that met DeepSeek's quite stringent criteria for a bona fide example but I finally came up with this which earned its seal of approval.
"The hack saw the editor."
We know that from a Sun-centred point of view the Earth goes around the Sun and the Moon round the Earth. If we could magically hover above the plane of the Sun-Earth-Moon system, remaining at rest relative to the Sun, what would the path of the Moon look like from that vantage point?
Intuitively I thought it would trace a loopy path, something like the dotted trajectory in my sketch below.
I was surprised to find out how wrong my intuition was. The actual path is like the one below, which was generated by an nice simulation from the University of Colorado [1].
This is not to scale of course, the diameter of the Earth is about 8,000 mi and the distance from the Earth to the Sun 93,000,000 mi so if the orbit were drawn to scale your screen would need to be (roughly) 40 m wide, or the Earth drawn so small it would be a speck.
[1] https://phet.colorado.edu/sims/html/gravity-and-orbits/latest/gravity-and-orbits_all.html
The sentence below (perhaps seen on a sign in a hospital) was discussed in a 1979 paper by Watson and Reich [1] and has attracted a good deal of interest in the intervening years.
What does it mean? Whoever wrote it presumably meant "Don't ignore a head injury however trivial it is", and that is what most people read it as, but if we unpick the wording carefully that is not what it literally means.
Compare it with "No citizen is too poor to be taxed" which says that no citizen is so poor as to be exempt from being taxed, i.e. all citizens are taxed. So it seems the hospital sign has a meaning opposite to the intended one.
A friend said she thought I must have some phobia about tidiness (what, me?) so I wondered if there is a word for such a condition. There wasn't but there is now, because I invented it.
Eutaxiophobia
Etymology : from Ancient Greek eu- (εὖ) "good" + taxis (τάξις) "arrangement" + phobia (φόβος) "fear"
Then I validated my new word by asking DeepSeek what it meant. It told me that it was not a commonly recognised word but if it existed it would mean "a fear or aversion to orderliness or tidiness", which fits the bill perfectly.
It's possible I am not the only person with this particular phobia.
Easy really, it’s just comma sense.
oscine : pertaining to songbirds
This word came into English from Modern Latin in the late 19th century. The ancient Latin word is oscen, whose elements according to Etymonline are ob- and canere "to sing". These in turn have Proto-Indo-European origins, epi-, which has a broad prepositional meaning of spatial nearness and kan-, "to sing".
Other words that seem to be from kan_ include accent, charm, descant, enchantment and Carmen, and many others.
Oscine is a rare word. I came across it in Times 2 Word watch column and I'd never seen it before. It only occurs on average 0.01 times per million words. So in this blog post it has come up with a frequency that would normally only appear once in every 200 million words.
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