613 reputation
314
bio website
location
age
visits member for 4 years
seen 1 hour ago

Oct
17
comment What are the odds of hitting exactly 100 rolling a fair die
@David Your intuition is good here, but not quite correct. Try working the problem with a total sum of 8 (which appears to be the smallest non-trivial case) and you will see where the bugaboo occurs
Oct
17
comment Suggestion for Math Movies
I can't believe no one's mentioned Story of 1, although it is fairly basic.
Oct
15
comment Trouble understanding case analysis (proof by cases)
Because the square root of 5 is between 2 and 3.
Oct
15
comment How can I prove that (B and (A implies B)) is equivalent to B?
Hmmm... you still need parentheses (and did you just edit your answer after my comment? <G>)
Oct
15
comment How can I prove that (B and (A implies B)) is equivalent to B?
Consider two cases: B is true and B is false. Or, to make things slightly harder, consider these two cases instead: A is true and A is false.
Oct
15
comment How can I prove that (B and (A implies B)) is equivalent to B?
Are you sure about your first step? Don't you have to distribute the first b across the parentheses? I realize you'll just get b V b (which is b), but it looks like you just removed the parentheses, so it's unclear what logic rule you were using.
Oct
8
comment Calculation of $\int_{0}^{\frac{\pi}{4}}\tan^{-1}\sqrt{\frac{\cos 2x }{2 \cos^2 x}}dx$
This doesn't help, but the numerical value is roughly 0.41123351671205660911810379166150629730473746630197, and, according to oldweb.cecm.sfu.ca/cgi-bin/isc/… this doesn't appear to be a "well known" number.
Oct
7
comment Name of a certain set
Perhaps see also math.stackexchange.com/questions/61613/…
Oct
7
awarded  Citizen Patrol
Jul
2
awarded  Curious
Jun
11
awarded  Yearling
Mar
29
awarded  Nice Question
Mar
26
comment Normal distribution percentile calculation
Intuitive answer: 97.8% (less than 99%) of the parcels will be less than 2 deviations above the mean. 2 deviations above the mean is 19 pounds, so 16.465 can't possibly be right (even excluding the extra pound). Incidentally, this model isn't very good because it states that some packages will weigh less than 0 pounds.
Mar
26
comment love in an elevator
Possibly simpler: combined weight of 16 people averages 1200kg with a standard deviation of 40kg (variance increases linearly with the number of people, so standard deviation increases with the square root of the number of people). As noted above, the chance this exceeds 1140kg is the chance the standard normal variable exceeds -1.5 standard deviations, or about 0.9332 as noted above
Mar
26
comment love in an elevator
@JoelReyesNoche What's love but a second-hand emotion?
Mar
26
comment What is the cartesian equation of $r = 1 + r \sin(\theta)?$
Well, r^2 = x^2 + y^2 and tan(theta) = y/x, and go from there.
Mar
13
accepted Population average age decreases with births AND deaths (kind of)?
Mar
13
comment Population average age decreases with births AND deaths (kind of)?
Of course! As long as the age decrease I describe is slower than the flow of time, the average age still increases. I will approve this answer as soon as stack lets me.
Mar
13
asked Population average age decreases with births AND deaths (kind of)?
Feb
28
answered Deriving the Area of a Sector of an Ellipse