Today's Topics (June 2020)

debbie

Tue 6/16/20

Show that all the terms in the sequence $ 10001, 100010001, 1000100010001, \ldots $ are composite.
A quadrilateral is inscribed in a circle of radius $200 \sqrt{2}$. Three of the sides of this quadrilateral have length $200.$ What is the length of the fourth side?
I couldn't control my other broken calculator, so I bought a new one. I typed too many numbers in it, and it broke. $36$ gives $105, 82$ gives $486, $ and $29 $ gives $196.$ What number did I put in if the output is $153?$

debbie

Topics Wed 6/17/20

$111111111^2$ ; also, the version with eleven $1'$s
Roman Numerals
What's the name of a $360$-sided shape? (A triacosiahexecontagon, apparently, according to our audience!)
"How old is your son?" asked a man to his neighbor. "My son is five times as old as my daughter, and my wife is five times as old as my son. I am twice as old as my wife, whereas my grandmother, who is celebrating her $81$-st birthday, is as old as all of us put together." How old is the man's son?
My eye sees things at $30$ frames per second, so why is my $40$-frame-per-second video game laggy?
What frame rate is our life going at?
What frame rate is this video?
How did you get the idea to start this livestream?
"I am about $79.2$% sure that Prof. Loh won't see this.
Today is my birthday, and I have a problem about it: If there are $200$ people watching this live stream, what is the chance that at least $2$ of them have the same birthday?

RZ923

@debbie
—According to Wikipedia

debbie

@RZ923 Awesome, thank you for looking this up.

debbie

Topics from the Friday 6/19/20 live stream

Please explain the metallic ratios (gold, silver, etc.)
Is the myth true that the golden ratio appears in the Mona Lisa?
Didn't Da Vinci invent the Ornithopeter or whatever it's called? (Helicopter-like flying machine.)
One fourth of the population of a newly discovered planet have 4 legs. The rest have two legs. There are 60 legs total. How big is the population of the newly discovered planet?
If $ a + b + c = 10, a \times b \times c = 30,$ what is the value of $a^2 \times b^2 \times c^2?$ (Many possible solutions.)
Prove that if you square root any positive number (it doesn't have to be an integer, and it can't be 0,) an infinite number of times, you will get 1.
There is a toilet roll whose radius is $4$ and the "empty part" of the roll has a radius of $1.$ What is the length of the paper if we unroll the toilet paper? (Audience contributed helpful numbers: 375 sheets per roll in Singapore, 276 layers in one roll (counted by hand), 0.0004 inches per sheet)
How many bananas do you eat every day? (Answer: 1)
Do you use bootstrap for your websites?
How do you build a thermonuclear missile with a launch site using only metal and 10 pounds of plutonium? I need to know by Friday because that's when my geometry is due.
Why do you love math?

RZ923

@debbie
I was sorry I couldn’t attend today’s livestream.
For the question where:
$a+b+c=10$
$a\times b\times c=30$
$a^2\times b^2\times c^2=?$
I don’t get why you put “unsolvable”.
Shouldn’t it be:
$a=2,b=3, c=5$(or some other way around)
$a^2\times b^2\times c^2=4\times 9\times 25=900$?

debbie

@RZ923 Thanks for your comment! I actually meant that there are many solutions. The set of equations doesn't uniquely determine a single solution. So "unsolvable" isn't exactly the right word. For example, another solution is $a = \sqrt{3}i, b = -\sqrt{3}i, c = 10.$ Then we would have

$$ a + b + c = \sqrt{3}i - \sqrt{3}i + 10 = \boxed{10} $$
$$ a \times b \times c = \sqrt{3}i \times -\sqrt{3}i \times 10 = 3 \times 10 = \boxed{30} $$

Thanks for pointing this out.

debbie

Newport Math Club Knights of Pi Math Tournament Special Livestream Saturday 6/20/20

Questions from Newport Math Club:

Find the sum of the digits of the sum $ 9 + 99 + 999 + 9999 + … + 999999999 $ (nine 9’s)
Marisa draws a five-point star by extending the sides of a convex pentagon with all angles less than 120°. What is the sum of the angles of the points of her star, in degrees?
How many solutions does the equation $2^x = x^2 $ have for some real value of $x?$
If everyone is connected to all the people they’ve ever greeted, how many degrees of separation is the world away?
If we met an alien civilization and exchanged mathematics, what maths do you think would be similar, and what would be different? Would they have things like real numbers?
What does convex mean?
Compare CMU and Caltech
Can you describe your stack from Caltech's Ditch Day?
Would you rather win the Nobel Prize or "invent" math?
How can you predict when a popsicle will melt?
How does base $\frac{1}{37}$ work?
Would you rather have cake, ice cream, or cupcakes for the rest of your life?
Have you ever participated in an Improv Troupe? If so, how was your experience?
If a jet goes 90 mph, and a monkey goes 5 mph, and if the monkey drops from a tree it goes 4 miles per hour. How fast does a banana go if the monkey jumps for 5 hours?
What would happen if someone used a sonic boom on NOVID? (Relates to this BBC documentary about pistol shrimps)
How do I make a nuclear reactor?
Can you give some advice on trading? (And some mention of how oil prices went negative in April...)
How do I infiltrate the ISS (International Space Station)?
Metric or Imperial system for measurements? (foot, inch, barley grain = smallest unit of weight in the troy and avoirdupois systems, equal to $\frac{1}{5760}$ of a pound troy, and $\frac{1}{7000}$ of a pound avoirdupois (approximately 0.0648 grams)
Besides math and programming, do you have other hobbies that you do in your free time?
Can someone hack NOVID?

divinedolphin

@debbie said in Today's Topics (June 2020):

How do I infiltrate the ISS (International Space Station)?

haha

sqwishy

@divinedolphin haha

The Blade Dancer

Ooh can I go when you do infiltrate it

debbie

Topics from the 06/22/20 live stream

Find the number of three-digit numbers such that the digits are in strictly increasing order from left to right. For example, $123, 489,$ etc.
We have a suggested expression, $9 \times 9 \times 8,$ for the above question, which isn't actually correct. Let's try to find a question that would give $9 \times 9 \times 8$ as an answer!
What would happen if all the water in a rainstorm came down in one huge drop? (It was raining hard )
In the right triangle $\bigtriangleup ABC, AC = 12, BC = 5,$ and angle $\angle C$ is a right angle. A semicircle is inscribed in the triangle on side $AC$ at the right angle. What is the radius of the semicircle?
Why is it named the Pythagorean Theorem?
How many $0$'s does the base ten numeral $58!$ end with when written in base $12?$
Which award is considered to be like an Oscar for math?
How to find the volume of a banana
What is Avogadro's Number?
The area of a cuboid is $150 \text{ } \text{m}^2.$ What is the height of the cuboid if its volume is $1800 \text{ } \text{m}^3?$

debbie

Topics from the Tues 6/23/20 live stream

If $k$ and $n$ are integers and $ \left( 3^{2006} + 2006 \right)^2 - \left( 3^{2006} - 2006 \right)^2 = k \times 3^n,$ where $k$ is not divisible by $3,$ compute $\frac{n+k}{2006}.$
What is the value of $\frac{2020^2 - 2012^2}{2017^2 - 2015^2}?$
Do you consider yourself a mathematician, mathemagician, or math teacher/coach?
The positive integer $n$ is between $1$ and $20.$ Milly adds up all the integers from $1$ to $n$ inclusive. Billy adds up all the integers from $n+1$ to $20$ inclusive. Their totals are the same. What is the value of $n?$
Are eggs good for you?
On an algebra quiz, $10\%$ of the kids scored $70$ points, $35\%$ got $80$ points, $30\%$ got $90$ points and the rest scored $100\%.$ What is the difference between the mean and the median of the students' scores?

debbie

Topics from the Wed 6/24/20 live stream

The lengths of the sides of a triangle in inches are three consecutive integers. The length of the shortest side is $30\%$ of the perimeter. What is the length of the longest side?
The base-3 repeating decimal $0.\overline{12}_3$ is equivalent to what base ten common fraction?
How do you build a tank out of wood?
How many bananas do you need to make enough radiation for a nuclear missile?
How many bananas do you need in order to die of radiation?
Can you do percents with binary?
Did you guys know that $64$ is the smallest positive integer that is both a perfect square and perfect cube besides $1?$
There is a ten-digit number with the property: the top digit is divisible by $1,$ the $2$ top digits are divisible by $2,$ and so on, until the top-10 digits are divisible by $10.$ What is the number? (Variation: What if each digit was only used once?)
Let $ \bigtriangleup ABC $ be an equilateral triangle of length $3$ that has mirrors as sides. What is the shortest distance a light beam, starting from point $A,$ would have to travel to end at point $B?$ (From the 2015 Knights of Pi Math Tournament, run by the Newport Math Circle.)
If you go to the movies and you're paying, is it cheaper to take one friend to the movies twice, or two friends to the movies at the same time?
How do you push yourself to solve more problems? Of late, I've been acting a bit lazy, but I've realized that I can do more, but I'm unable to push myself to complete a problem in the stipulated time.

RZ923

The one with the ten digit number was my question I logged.
Sadly I couldn’t come today.

debbie

@RZ923 Yes, I replied to your other post in "Early Bird Question"! Sorry that you weren't there, but at least you can watch the replay!

debbie

Topics from the Wed 6/24/20

Three points are chosen randomly and independently on a circle. What is the probability that all three pairwise distances between the points are less than the radius of the circle?
I am an odd number. Take away a letter and I become even. What number am I?
I add $5$ to $9$ to get to $2.$ This is correct, so how is this possible? (Answer: On a clock.)
Is there any math in games such as Minecraft?
Find three positive rational numbers $a, b,$ and $c$ such that $a + b + c = a \times b \times c = 7.$
What three numbers, none of which is zero, give the same result no matter whether they're added or multiplied?
At what points on Earth can you travel in a perfectly straight line and go due east at the same time?
Can you arrange four $9$'s to make it equal to $100?$

debbie

Topics from the Friday 6/26/20 live stream

If $f(0.25) = 0.5 $ and $f(0.5) = 0.5,$ how can we find $f(x)?$ (Lagrange Interpolation)
Po the cat is catching fish! He has a $\frac{1}{3}$ chance of catching a salmon, $\frac{1}{8}$ change of catching a trout, and $\frac{1}{10}$ chance of catching a hallibut. How much chance does he have of catching a shrimp?
What is $x + x - x^{-2}$ if $x = 5?$
How many people do we need to watch the stream for Ask Math Anything to continue?
If $a + b = \frac{a}{b} + \frac{b}{a},$ find $a^2 + b^2.$
What fractions are equivalent to $ \frac{1}{2}?$ Can you list all of them?
Suppose you have $3$ variables; is it possible to have only $2$ equations with a definite answer for all variables?
What is a real number?
How is it possible to have an irrational measurement?
We know that in a right-angled triangle, $ \text{hypotenuse}^2 = \text{base}^2 + \text{perpendicular}^2.$ What will be the relation if we cube them?

debbie

Topics from the Saturday 6/27/20 live stream

What professions are fit for math majors?
Are people who are blind better at hearing?
Do you recommend looking at the MATHCOUNTS School Handbook every day?
Can we talk or yell something in ultrasound?
What types of things should we memorize?
What do you teach at CMU?
What is an undergraduate student?
Who invented your theme song?
Do you like China's education system, with lots of homework, memorization, and competition?

debbie

Topics from the Monday 6/29/20 live stream

What is the easiest way to solve this question? "A printer users 300 digits to number the pages of a book. How many pages are in the book? (The book starts at Page 1.)
The product of two prime numbers is 9 more than their sum. What is their absolute difference?
What is the difference between $ \pi $ and $ \phi?$ (Relates to the golden ratio!)
In a sequence the terms are $2, 6, 12, 72, \ldots$ where, starting with the 3rd term, every term is the product of the last two terms. If the $9^{\text{th}}$ term is $ 2^a * 3^b,$ what is $a + b?$
What's the difference between the Po-Shen Loh ratio and the Daily Challenge ratio?
If you had to eat one of these, which one would you eat? Crispy Apple, Savory Popcorn, or Sweet Energy Bar?
How can you make the following equation true by drawing only one straight line? $ 5 + 5 + 5 = 550$
If a truck goes at a speed of $2^x $ mph on the $x$th minute, then how many miles does it go in $1$ hour?
Use eight $8$'s and the operations of addition, subtraction, multiplication, division, exponentiation, factorials and square roots to make $1000.$
What is the max distance between two watchers of today's AMA (Ask Math Anything)?