3 ms·

Memorizing a set of numbers doesn't really feel like a shorthand way to remember those numbers. Did you know about the 3.14 rule? It's a way to remember the fir

Memorizing a set of numbers doesn't really feel like a shorthand way to remember those numbers. Did you know about the 3.14 rule? It's a way to remember the first three digits of pi are 3.14.

sroussey 4y ago
Which is, I don’t know — ironic? — because pi rounded to two decimals is 3.15.
- elijaht 4y ago
  No it’s not- it’s 3.141, which rounds to 3.14
  - midasuni 4y ago
    It’s 3.14159 3.1416 3.142 3.14 3.1 3
    - sroussey 4y ago
      Oh, I feel dumb. Some reason I had it memorized without the 1: 3.1459 — for years! Decades! I wonder what tests I screwed up in collage!
- scythmic_waves 4y ago
  No pi is 3.14159... which is 3.14 when rounded.
- karmakaze 4y ago
  The 3.2 rounding of Pi in an Indiana bill[0] is also quite infamous, which confusingly had other values of Pi for use in different contexts. [I'm a Tau touter myself.] [0] https://www.straightdope.com/21341975/did-a-state-legislature-once-pass-a-law-saying-pi-equals-3 https://www.straightdope.com/21341975/did-a-state-legislatur...
- euroderf 4y ago
  The approximation 355/113 has nice pairs of odd digits.
bumbledraven 4y ago
An more useful thing to remember is Shah's approximation, which estimates the area under the standard normal curve from 0 to a point 𝑧 on the x axis as follows: • 𝑧(4.4 – 𝑧)/10 when 0 ≤ 𝑧 ≤ 2.2 • 0.49 when 2.2 < 𝑧 < 2.6 • 0.50 when 2.6 ≤ 𝑧 Shah's approximation is accurate to within roughly ±½%. Examples: - The area under the standard normal curve within 1 standard deviation of zero is approximately 2(1(4.4 – 1))/10 = 0.68. (The factor of 2 is there to get the area on both sides of zero). - The area within 2 standard deviations of zero is approximately 2(2(4.4 – 2))/10 = 0.96. - The area within 3 standard deviations of zero is approximately 1 (because 2.6 ≤ 3). - The probability of sampling from the standard normal distribution and getting a value less than 1.5 deviations above the mean is approximately 0.5 + 1.5(4.4-1.5) = 0.935. (The 0.5 term is there because we need to include the area to the left of 0, and Shah's approximation only counts the area to the right of zero.) Reference: Arvind K. Shah (1985) A Simpler Approximation for Areas under the Standard Normal Curve, The American Statistician, 39:1, 80, DOI: 10.1080/00031305.1985.10479396 (https://twitter.com/jordancurve/status/958026273149915136/photo/2 https://twitter.com/jordancurve/status/958026273149915136/ph...)

Memorizing a set of numbers doesn't really feel like a shorthand way to remember those numbers. Did you know about the 3.14 rule? It's a way to remember the first three digits of pi are 3.14.

sroussey 4y ago

Which is, I don’t know — ironic? — because pi rounded to two decimals is 3.15.

elijaht 4y ago
No it’s not- it’s 3.141, which rounds to 3.14
- midasuni 4y ago
  It’s 3.14159 3.1416 3.142 3.14 3.1 3
  - sroussey 4y ago
    Oh, I feel dumb. Some reason I had it memorized without the 1: 3.1459 — for years! Decades! I wonder what tests I screwed up in collage!
scythmic_waves 4y ago
No pi is 3.14159... which is 3.14 when rounded.
karmakaze 4y ago
The 3.2 rounding of Pi in an Indiana bill[0] is also quite infamous, which confusingly had other values of Pi for use in different contexts. [I'm a Tau touter myself.] [0] https://www.straightdope.com/21341975/did-a-state-legislature-once-pass-a-law-saying-pi-equals-3 https://www.straightdope.com/21341975/did-a-state-legislatur...
euroderf 4y ago
The approximation 355/113 has nice pairs of odd digits.

bumbledraven 4y ago

An more useful thing to remember is Shah's approximation, which estimates the area under the standard normal curve from 0 to a point 𝑧 on the x axis as follows: • 𝑧(4.4 – 𝑧)/10 when 0 ≤ 𝑧 ≤ 2.2 • 0.49 when 2.2 < 𝑧 < 2.6 • 0.50 when 2.6 ≤ 𝑧 Shah's approximation is accurate to within roughly ±½%. Examples: - The area under the standard normal curve within 1 standard deviation of zero is approximately 2(1(4.4 – 1))/10 = 0.68. (The factor of 2 is there to get the area on both sides of zero). - The area within 2 standard deviations of zero is approximately 2(2(4.4 – 2))/10 = 0.96. - The area within 3 standard deviations of zero is approximately 1 (because 2.6 ≤ 3). - The probability of sampling from the standard normal distribution and getting a value less than 1.5 deviations above the mean is approximately 0.5 + 1.5(4.4-1.5) = 0.935. (The 0.5 term is there because we need to include the area to the left of 0, and Shah's approximation only counts the area to the right of zero.) Reference: Arvind K. Shah (1985) A Simpler Approximation for Areas under the Standard Normal Curve, The American Statistician, 39:1, 80, DOI: 10.1080/00031305.1985.10479396 (https://twitter.com/jordancurve/status/958026273149915136/photo/2 https://twitter.com/jordancurve/status/958026273149915136/ph...)