







The inverse square law 
20180605 

From Amy:
Question about inverse square law ;
Hi, I'm trying to understand some nuances about this law and
have been reading about it a lot online and trying out some homework
for personal interest (hobby )  not school related.
I understand that the simple formula is ; 1/d^2
I was wondering about what appears to be an oddity to me, that
I came across when I was working with a test example I found at this
link ;
http://www.softschools.com/formulas/physics/inverse_square_law_formula/82/
The problem that caught my interest was this one on that page ;
"1) If a bright flashlight has a light intensity of 15.0 candela at a distance 1.00 m from the lens, what is the intensity of the flashlight 100.0 m from the lens?"
So I have a few different questions about this, but the most important
one is, what does it mean if we replace the "1" in ; 1/d^2 with a different value such as a ratio in the form of a decimal value, so instead we have something like this ;
0.75/d^2
???
Does this ratio represent a curve then?
I am thinking that the "1" in the normal formula represents a straight line
Some of the links I was researching ;
http://wisptools.net/book.php?c=3&s=2
http://www.softschools.com/formulas/physics/inverse_square_law_formula/82/
https://www.ndeed.org/GeneralResources/Formula/RTFormula/InverseSquare/InverseSquareLaw.htm Answered by Penny Nom. 





The tens digit of a number is five times the unit digit 
20160519 

From sanjeev: The tens digit of a number is five times the unit digit. Find the number? Answered by Penny Nom. 





A two digit number 
20150821 

From Cameron: Write the 2 digit number that matches the clues.
My number has a tens digit that is 8 more than the ones digit. Zero is not one of my digits.
My number is ________. Answered by Penny Nom. 





A two digit number 
20110301 

From jhoanna: the sum of the digits of a two digit number is 10. The value of the number is 16 times the units digit.Find the number. Answered by Penny Nom. 





The tens digit of 0! + 1! + 2! + 3! + 4! .............+9999! + 10000! 
20090123 

From Kaylyn: determine the tens digit for the expression:
0! + 1! + 2! + 3! + 4! .............+9999! + 10000! Answered by Robert Dawson and Penny Nom. 





Girls, cats and kittens 
20080516 

From leria: There are 7 girls in a bus.
Each girl has 7 backpacks
In each backpack, there are 7 big cats
For every big cat, there are 7 little cats.
How many legs are there in the bus? One hint? it's a 6 digit number Answered by Penny Nom. 





Women, cats and kittens 
20080212 

From Paige: There are 7 women on a bus. Each has a backpack. In each backpack there are seven cats. Each cat has seven kittens. How many legs are there total on the bus? Answered by Penny Nom. 





Tens and ones 
20070916 

From julia: My son has come home with a math question "what i know about 10s and 1s" we're totally stumped any information you can provide would be greatly appreciated Answered by Harley Weston. 





The tens digit 
20070821 

From Arul: Hi..
Please help me on this question..
Sequence 2, 7, 22,…after the first three terms, each term is three times the previous term plus 1, a(n+1)=3an + 1. What is the sum of tens digit 33rd and tens digit of the 35 term? Answered by Penny Nom. 





The tension in a single strand of wire 
20070813 

From Gene: Seeking an equation that calculates the tension in a single strand of wire or rope. Conditions: the wire is fixed at both ends, A known weight is suspended from the center of the span. The weight will dipslace the strand downward some distance Y. Let the distance between the fixed ends be X= 500mm. Weight W=0.5kg. Original tension in the strand is T= 10 newtons.Your help sincerely appreciated. Answered by Gabriel Potter and Stephen La Rocque. 





What is the intensity 5m below the surface? 
20070331 

From david: I have this question which I am supposed to set it up and solve as a differential equation. I know how to solve the diffrential equation but I am having hard time understanding this question. Here is the question: The intensity of light in the ocean decreases the deeper you dive. In fact, the rate at which the intensity decreases is proportional to the current intensity. Setup the corresponding differential equation and solve for I(Y), the intensity I as a function of current intensity Y. If the light intensity 2m below the surface is 25% of the intensity at the surface, what is the intensity 5m below the surface. Can you please explain to me what does it mean by current intensity and how do I set this equation up. Thanks for the help. Answered by Penny Nom. 





The tens digit of a really large number 
20070305 

From Sai: How can i find the tens digit of a really large number? i was gven 63^15 + 15^63 in a competitive exam. Answered by Penny Nom. 





Percentage increase in sound intensity 
20060129 

From David: I am doing some emotion response mapping.
Being a composer I know how to push the heart beat tempo by a % increase of BPM in my music. I want to know how to calculate an increase in intensity of sound. Now I have 60 decibels. I want an increase of intensity by a factor n% with out going over 156 decibels.
Answered by Penny Nom. 





The digits in 349 
20030912 

From Franik: in the number 349, which number has the least value, and why? Answered by Penny Nom. 





oneths 
20020430 

From Logan: why are there tenstenths hundredshudreths, but not oneths if that made no sense then how about this why does everything have two ways of saying things like tens and tenths but not a oneths Answered by Claude Tardif. 





0! + 1! + 2! + 3! + ... + 2000! 
19991021 

From Melissa: My name is melissa. I am a 9th grade student I am having trouble finding out how to do this: What is the tens digit of 0! + 1! + 2! + 3! + ... + 2000! I know how to find these, but my calculator cant go any higher than 69! Is there any way i can do this problem? Answered by Penny Nom. 





isomorphisme 
20000810 

From Romain Kroes: Pour les beoins d'un ouvrage d'économie que je suis en train de terminer, pouvezvous me dire qui est (sont) l'inventeur de l' "isomorphisme" en mathématiques (calcul tensoriel)? Answered by Claude Tardif. 

