blonde poker forum

Was mightily impressed with Mully & Tighty yesterday, especially on those "number" questions.

I could make a reasonable guess at the capacity of a football stadium owned by a successful club - if we said 50,000, we can't be THAT far out, but some of the other questions seemed impossible.

Then Team Clever Clogs - Mully, aided & abetted by Posh Alex - introduced us to  the wonders of "Fermi Problem".

https://en.m.wikipedia.org/wiki/Fermi_problem


For those who cba to read tall the gumf, here's the example on wiki......


The classic Fermi problem, generally attributed to Fermi, is "How many piano tuners are there in Chicago?" A typical solution to this problem involves multiplying a series of estimates that yield the correct answer if the estimates are correct. For example, we might make the following assumptions:

1.There are approximately 9,000,000 people living in Chicago.

2.On average, there are two persons in each household in Chicago.

3.Roughly one household in twenty has a piano that is tuned regularly.

4.Pianos that are tuned regularly are tuned on average about once per year.

5.It takes a piano tuner about two hours to tune a piano, including travel time.

6.Each piano tuner works eight hours in a day, five days in a week, and 50 weeks in a year.

From these assumptions, we can compute that the number of piano tunings in a single year in Chicago is
(9,000,000 persons in Chicago) / (2 persons/household) × (1 piano/20 households) × (1 piano tuning per piano per year) = 225,000 piano tunings per year in Chicago.

We can similarly calculate that the average piano tuner performs
(50 weeks/year)×(5 days/week)×(8 hours/day)/(2 hours to tune a piano) = 1000 piano tunings per year per piano tuner.

Dividing gives
(225,000 piano tunings per year in Chicago) / (1000 piano tunings per year per piano tuner) = 225 piano tuners in Chicago.

The actual number of piano tuners in Chicago is about 290


 

So let's test it.

Here's your question.

How many female poker players who live in London will play online poker tonight? (Thursday 30th September).


I'll give it a bash, let's see if anyone else dare make the same fools of themselves as I am about to.

 

317

The population of London is somewhere around 8.8 million.

50%ish of these are women, 4.4m

80% of these are over 18 years old and legally allowed to gamble in the uk, 3.6m

1% of women play poker, 36,000

50% of poker players play online. 18,000

People will play 2 nights per week online, 2/7 x 100 = 28.5% chance of playing on a random night.

28.5% of 18000 = 5130

My guess is 5130 women will play poker online in London tonight.

do you have the answer to this?

ideally you want there to be an actual provable answer.....


anyway london has 8.5m people, roughly

lets say 4.25m are women

lets also say that london is younger than the rest of the country, on average

now we have to make an estimate of

a) how many of london's women play poker online

and b) of that number how many would be playing tonight

i remember a piece of work a few years ago that said there were 250,000 or so uk online poker players

most of them are male?

lets say 25% are female 60-70,000

of that 60-70,000...london is 8.5/64m of the uk population = 13% of total

13% of 65,000 say is 5,000

how many of those 5000 would be playing tonight

impossible to say but lets say its sub 50%.

i'll fermi 2,000 as the answer

but the question isn't a great example

How many female poker players who live in London will play online poker tonight? (Thursday 30th September).


I'm not entirely sure if it is critical to get all the "reducers" in the correct order, but anyway, off we go.

These are all "my best guess", no google referencing.

12 million people live in London.

20% are under age, 20% are too old, 10% are unwell, hospitalised or in prison, 20% don't have internet or a computer at home.

So we are down to 30% of 12 milly which = 3.6 million.

How many of them play online poker? 1 in 100 seems too many, 1 in 200 seems not enough. Call it 1 in 150. So divide 3.6 milly by 150 & we get 24,000.

Female poker players equal around 5% of the total poker playing population. So, 24,000 x 5% = 1,200.

The average recreational poker player plays Online 2.5 times per week. (That's a rough industry standard).  They'll play less on Monday (MNF) or when CL is on telly (Tues & Weds), but more at weekends.  Let's leave it at 2.5 times per week.

So they will play every 2.8 days. So from that there is a 36% chance they will play on Thursday.  (I think....).

1,200 x 36% = 429.

So, that's the answer, 429.  Which is patently, obviously & clearly wrong.

No, I don't have a prove-able answer. If I did, I'd probably make the numbers "backfit".

In your example, which uses much different baselines to mine, 25% of poker players are female jumps off the page. Surely far, far less than 25%? If you made that 5% (five times less) your final number would be similar to mine. (That's called backfitting I suppose).

Think I'd best stick to NFL Last Longers.

yes we get similar answers if 5% of poker players are female. your estimate feels more right than mine on that.

Ironically you want to minimise the steps you take. Which seems counter intuitive because you think x% too much here is roughly cancelled by y% too little there, etc.

There's a good explanation for maths heads (multiply guesses is the same as adding their logarithms).

One way to think about it is it's like the bookie and his overround. The most teams (guesses) in your acca (fermi steps) the more money the bookie steals.

I think about 200 seems to be the answer. On a weekend it might be 800. Although tonight is a football night which surely has some effect.

Appreciate the explanation.

If you are between 200 & 800, my 429 does not look quite so bad. I might have got there incorrectly though. My teacher called them the "workings outs".

Ok, lets do an easier one. We can (reasonably) get a prove-able answer to this.

How many people in Great Britain own a mobile phone?

Or....


How many people in Great Britain own a motor car?

Tis like a technical version of ' What Johnny Lodden thinks. imo '

If the question is 'at least one mobile' (not the total number of of mobiles) then I'll go for a pretty simple two step approach:

60m people in Britain.
Mobile phone penetration something like 75%
45m mobile phone owners in Britain.

Fermi problems are useful to test dimensional analysis. They might not give you the correct answer but they are a quick way to test another answe, roughly. Eg for piano tuners you could think 2 or 20 or 200 or 2000 or 20000 piano tuners (or more!)

For mobile phones in Britain fermi isn't really 'useful' as an error catcher because you're never going to be an order of magnitude out (eg 200 not 2000, 450k not 4.5m) because mobiles (and cars) are so widespread.

The point of all of that being, if we predict that now there are 45m mobile phone owners in Britain and then launch a serious study and spent loads of money and it tells us 55m, we still don't know if we are right.

Where as if Fermi tells us there should be 225 piano tuners and we scientifically measure 4000 of them then something is wrong. There's a bias or something unaccounted for in either number and we can't use either with any great confidence.

Now that might sound silly for piano tuners in Chicago (surely we just count them rather than spend loads of money on a science experiment ) but for stuff like 'what's the tensile strength of this bit of metal' where finding out can be costly and expensive, it's good to be able to roughly 'sanity check' the number you get out.

How many people in Great Britain own a motor car?

UK Population is 65m

Population over 17 is about 55m (a bit less?)

how many people per household, on average? 4 sound about right?

55/4= lets say 14

average uk household 2 cars?

14*2=28m cars?


then google

"this is the list of summary results from the DVLA publication: “ At the end of 2012 there were 34.5 million vehicles licensed for use on the roads in Great Britain, of which 28.7 million (83 per cent) were cars.12 Apr 2013"





next question

“How many calories are in a supermarket?”

this was asked by Google to a Product Manager candidate to provide an answer face to face on the spot

not easy

5 billion.

Why are you working out over 17s and then ignoring them in your people per household?

70m now?
3.5 per household (lots of growth in single households)
Much less than 2 cars per house.  

For the female poker player in London question I came up with 160, and I have a better knowledge of the starting set of data than most people.


The way I'd go is estimate the average number of customers per week, assume each is buying for two people (lots of singles, lots of mums shopping for families). Say it's 5,000.

So 10,000 people are getting a good proportion of their weekly calorie requirement from this supermarket. Say it's 75% (25% from eating out, elsewhere).

Daily calorie intake of say average of 2,500 - 17,500 per week. 75% of that is about 13,000

13,000 x 10,000 = 130m

This assumes the supermarket carries an average of a week's stock on the shelves (stuff like milk, bread, fruit is less, cereals, tinned food etc has longer shelf life)

20 rows.  200 products per row, 3 deep on average.  8 high on average.  1000 calories per product.

100 million?

Could easily be out 10 fold though.  Would be easier if I googled first.

Got a five period day tomorrow so will do the piano tuners in Chicago with every single one and report back.....

Which of the following groups is your money on for the best guess?

Year 12 A Level Maths
Year 10 set 3
Year 11 set 4
Year 9 set 1
Year 8 set 4

Obv I can't give any further info than that

All sets are out of 5

Could well be the year 9s for me.

I think divergent thinking is a bit required here.

If the A-Level students have already had some exposure to dimensional analysis though then it will be them (been more than 10 years since my maths A-Levels so I have no idea what's on them anymore!)

Think I read somewhere that there are more mobile phones in the country than people.  We own over 1 each on average.

May have made that up but I thought that's what it said.

I have just googled and I am none the wiser.  Answer please

Google most certainly weren't interested in the actual answer. More the thought process, reasoning, defence of position, hierarchy of factors/information, etc.

Oxbridge interviews are notorious for this type of question; but in reality are a massive letdown/non-event.

I think rational thought is a hugely underrated tool for many, many historically successful companies so to see it so highly valued so quickly by some of the 'recent' success stories is refreshing.

Why do less women play online on champions league nights?

I would have thought if anything it could be more on these nights. Husband/partner has the TV so lady gets on computer and plays online.

That may be correct Greeky, & I suppose it depends on the order we do the equations, but the fact is, on all Northern Hemisphere online poker sites, traffic drops significantly on CL nights, just as it does during Monday Night Football. So the total number declines.

It may mean a small adjustment upwards to the number of female players, but we are still only ball-park, somewhere between 200 & 500. 100 more or less is not significant, imo.

Online poker sites also love transport strikes  - people stay at home & play Online - or really bad weather, ditto. In the UK, the record online poker traffic numbers occur during periods of heavy snowfall when we are all stuck at home, &, remarkably, on Bank Holidays. Boxing Day ids a HUGE day for Online poker. In the summer, when the weather is good, online numbers are awful. It's fascinating how many different things affect it.   

A suggested answer i saw was as follows

"There are approximately 12,000 supermarkets in the UK to feed 60 million people. The average calorie consumption per person is 2000, but figures suggest we waste 1/3 of what we buy . So we need to buy 182billion calories a day to feed Britain. That's 15million a supermarket. Supermarkets have stock in the back and on the shelves, replacing items as they're sold. Assuming each store has enough for 2 days (so they can replace as they go and resupply each night), that's 30million calories a supermarket. Then factor in restaurants, cafes, take-aways, work and school canteens and fast food. If we assume 7 meals a week are eaten there, rather than cooked at home, then that's 20million calories a supermarket."