Estimation quiz!

07302020, 10:54 AM
Post: #1




Estimation quiz!
This is from an old computer magazine: which is larger, the number of millimetres in a mile or the number of square yards in a square kilometre?
Any other quick numeric or numeracy quizzes to share? (Of course I liked this one because I got it right...) 

07302020, 11:27 AM
(This post was last modified: 07302020 11:30 AM by Paul Dale.)
Post: #2




RE: Estimation quiz!
Interesting problem. Being confident in both systems of units makes it easier.
Which is larger \( e^{\pi} \) or \( \pi ^ e \)? Pauli 

07302020, 01:00 PM
Post: #3




RE: Estimation quiz!  
07302020, 01:04 PM
Post: #4




RE: Estimation quiz!
They differ in their second digit...
Might the arguments to y^{x} have been backwards? Pauli 

07302020, 01:56 PM
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RE: Estimation quiz!
Which is larger eπ or πe?
isn't an estimation problem. 22 or 23 are the same for an estimate. 

07302020, 02:13 PM
Post: #6




RE: Estimation quiz!
(07302020 10:54 AM)EdS2 Wrote: which is larger, the number of millimetres in a mile or the number of square yards in a square kilometre? We can estimate relative size without multiplying 1 yard = (36 in) (25.4 mm/in) = 914.4 mm → 1 yard ≈ 1 m 1 mile = 1760 yard ≈ 1.760e6 mm // overestimated 10% 1 km^2 = (1e3 m)^2 ≈ 1e6 yard^2 // underestimated 20% Since 1.76 > 1.30, we have mile/mm > km^2/yard^2 (07302020 11:27 AM)Paul Dale Wrote: Which is larger \( e^{\pi} \) or \( \pi ^ e \)? e^x = 1 + x + x^2/2! + x^3/3! + ... ≥ 1+x x ≥ ln(1+x) → if x≠0, x > ln(1+x) ln(e^y) = y ln(y^e) = e*(1 + ln(1 + (y/e1))) ≤ e*(1 + (y/e1)) = y → if y≠e, ln(y^e) < y ⇒ e^y > y^e → e^pi > pi^e 

07302020, 02:24 PM
Post: #7




RE: Estimation quiz!
Or, even simpler:
Since e^x = 1 + x + x^2/2 +…, e^x > 1 + x if x>0 Take x = pi/e  1, x>0 because pi>e e^(pi/e1) > 1 + pi/e  1 e^(pi/e) / e > pi/e e^(pi/e) > pi (e^(pi/e))^(e) > pi^(e) e^pi > pi^e Cheers, Werner 

07302020, 02:34 PM
Post: #8




RE: Estimation quiz!
(07302020 02:24 PM)Werner Wrote: Or, even simpler: Clever! ;) Greetings, Massimo +×÷ ↔ left is right and right is wrong 

07302020, 03:10 PM
Post: #9




RE: Estimation quiz!
Another way, let f = ln(e^x/x^e) = x  e*ln(x)
f' = 1  e/x = 0 ⇒ x=e // locate extremum f'' = e/x^2 > 0 // 2nd derivative test, f(e) is minimum if f x ≠ e: f(x) > f(e) = 0 ⇒ e^x > x^e → e^pi > pi^e 

07302020, 04:20 PM
Post: #10




RE: Estimation quiz!
Albert and Werner: It's at times like this that I like to remind people this is exactly why we have calculators  when presented with a problem like this, we can carefully select the weapon of choice, perhaps an HP model not recently used, or an unusual competitive product, and bang it out.
With all due respect to your everobvious extreme math skills, I simply say: "Calculators gentlemen! The tool of discerning geeks everywhere" As for the expected question of how to reply if someone puts a gun to my head and demands I solve the problem without a calculator; my reply: "shoot" Bob Prosperi 

07302020, 05:37 PM
Post: #11




RE: Estimation quiz!
Two remarks: the proof I presented is not mine, I found it somewhere.
And: you win, Albert! Cheers, Werner 

07302020, 06:10 PM
Post: #12




RE: Estimation quiz!
Third way, using the fact that continuous compouding maximize capital growth.
For finite periods n, r>0: (1 + r/n)^n < e^r Let r = pi  e, n = e: pi^e = (e + r)^e = e^e * (1 + r/n)^n < e^e * e^r = e^pi → e^pi > pi^e 

07302020, 08:03 PM
Post: #13




RE: Estimation quiz!
(07302020 06:10 PM)Albert Chan Wrote: Third way, using the fact that continuous compouding maximize capital growth. Thanks Albert, that page is actually quite good. It's a clear and easy to follow derivation of the various interest formulae. [bookmarked] Bob Prosperi 

07302020, 10:25 PM
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RE: Estimation quiz!  
07312020, 12:01 AM
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RE: Estimation quiz!  
07312020, 01:26 PM
(This post was last modified: 07312020 01:28 PM by EdS2.)
Post: #16




RE: Estimation quiz!
Very nice view of the e^pi question!
For the headline (metric and imperial) I got it first by reckoning that both numbers were the same order of magnitude, and then by reckoning that miles are a bit on the large side for metric units, as are square yards, and both of those push in the same direction. The puzzle is from PCW magazine, in a puzzle feature called Leisure Lines. There's a corresponding book, but almost all the puzzles are not estimations. Here's the one I spotted which is: Quote:If you could fold a sheet of rice paper, a thousandth of an inch thick, successively doubling the thickness, 50 times over, how thick would the result be? [Content warning for that book: many cultural references have not dated well. Math and Logic Puzzles for PC Enthusiasts, by J. J. Clessa] 

07312020, 01:40 PM
Post: #17




RE: Estimation quiz!
\( 1000 \approx 2^{10} \), so \( \approx 2^{40} \) inches thick  thicker than the sun's diameter by a factor of 5 or 6.
Pauli 

07312020, 02:33 PM
Post: #18




RE: Estimation quiz!
(07312020 01:40 PM)Paul Dale Wrote: \( 1000 \approx 2^{10} \), so \( \approx 2^{40} \) inches thick  thicker than the sun's diameter by a factor of 5 or 6. Well, no. 2^40 inches are some 27.9275 million kilometers, and the sun's diameter is about 1.3927 million kilometers, so the factor is ~20. Your estimation was wrong by some 300400%. V. Find All My HPrelated Materials here: Valentin Albillo's HP Collection 

08012020, 01:09 AM
Post: #19




RE: Estimation quiz!
Thanks for the correction.
Regardless, it is a huge number. Pauli 

08012020, 06:48 AM
(This post was last modified: 08012020 06:49 AM by EdS2.)
Post: #20




RE: Estimation quiz!
Very good. I thought Pauli's estimate interesting  evidently each of us have our favourite yardsticks. For me, the distance to the Moon is the biggest one(*) in miles, at a quarter of a million. I don't (didn't) even have a figure in mind for the size of the Sun. I think in future I'll count it as nearly a million miles. (I'm from the UK but old enough to be mostly unmetricated.)
A bit of mental arithmetic, reckoning 30 inches to the yard and 1500 yards to the mile, and 30*30 about 1000, got me to the answer of 20 million miles, which isn't too far off. (I'd like to make a joke comparing a Pauli estimate to a Fermi estimate, but I can't do it.) (*) Oh, no, I do have the figure 93 million miles for the distance to the Sun. Perhaps the earliest large number I came across. And two digits of precision! 

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