My birthday this year (2011) is on a Friday. In most years, one’s birthday the following year is on the subsequent day of the week, and in that pattern, my birthday next year (2012) it is on a Saturday. However, due to 2012 being a leap year, my birthday in 2013 will be on Monday […]

I’m not a very smart man. I’m trying to count how many years I’ve been working at my new job. I started in May 2011. If I count the years separately, I get that I’ve worked 4 years – 2011 (year 1), 2012 (year 2), 2013 (year 3), 2014 (year 4). But if I count […]

As previously there were a method to find the date from the year 1893 to 2032 , which is very difficult to take a list of table always . Is there any other easy way to find the day of any date ?

In Summer Wars the main character (he is a mathematician) calculates the day of the week of someone’s birthday (19/07/1992 is Sunday). I know (very) basic modular arithmetic but I can’t figure out how to do it. Can someone point me to the right direction? It seems fun to do.

There are many descriptions of the “birthday problem” on this site — the problem of finding the probability that in a group of $n$ people there will be any (= at least 2) sharing a birthday. I am wondering how to find instead the expected number of people sharing a birthday in a group of […]

Everyone knows Friday the 13th is regarded as a day of bad luck. Why does every year have at least one of this bad day?

Intereting Posts

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$\sqrt a$ is either an integer or an irrational number.
The “Bold” strategy of a single large bet is not the best Roulette strategy to double your money
number of primitive Pythagorean triangles whose hypotenuses do not exceed n?
Showing $x^8\equiv 16 \pmod{p}$ is solvable for all primes $p$
Simplest or nicest proof that $1+x \le e^x$
Differentiability of $f(x) = x^2 \sin{\frac{1}{x}}$ and $f'$
Finding $26$th digit of a number.
Proving that if $A^n = 0$, then $I – A$ is invertible and $(I – A)^{-1} = I + A + \cdots + A^{n-1}$
understanding $\frac{\partial x}{\partial y}\frac{\partial y}{\partial z}\frac{\partial z}{\partial x}=-1$
Let $a,b \in \mathbb{Q^{+}}$ then $\sqrt{a} + \sqrt{b} \in \mathbb{Q} $ iff $\sqrt{a} \in \mathbb{Q}$ and $\sqrt{b} \in \mathbb{Q}$
Proving $\phi(m)|\phi(n)$ whenever $m|n$
In my textbook,the coordinate (x,y) by sine and cosine addition formula seems to form a circle,is that a coincidence?
Two distinct tangents are drawn to cubic
Advanced beginners textbook on Lie theory from a geometric viewpoint