Math / Science

The Math / Science topic primarily includes discussions of mathematics, physics, statistics and economic analysis, but also biology, chemistry and other sciences.

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The big terms of BigO Notation

I want to drill down into BigO, but hope to do so from a usefulness perspective. So, regarding making low-level algorithms more performant, for example. Or, from a memory management view...

Suggested topics to read up on? And a site where I can read this?

The diagonal length of the square from corner to corner is 19 inches.  Formula for the 4 equal sides of the square.
Hi there.

I have trouble how to do this in STATA: I have a dataset with response (BOR) for the patients. The variable BOR can be CR, PR, SD, PD or NE. Each patient can be in either arm A or B. I need to make a table in STATA with the distribution of BOR on arm A and B, and I also need to calculate a p-value (log-rank) and Hazard ratio for each value of BOR.
Anyone who can tell me how to do this in STATA? If not STATA, when maybe the codes in an altertative statistics software? It's probably very much alike.
Thank you in advance.

Best regards

Why does a football fly better with a good spiral?
Hello and Good Evening Everyone,

             After reading this rather scientific intriguing article at , I have the following question:  Is it possible to bring back to life an extinct species of tree by simply planting a seed of this extinct tree?   It seems to me that the seed would be dead and can not be expected to bring to life any species of tree or living plant.  But, could the seed itself be treated somehow scientifically and then planted in order to bring to life this extinct tree as indicated within the article?  Unfortunately, my scientific knowledge is merely limited to the general courses required to obtain my college degree in addition to never having a botany course per se.

              Any shared thoughts regarding this question will be appreciated.

              Thank you

How many triangles are there

Can anyone figure out my grandson's Year 4 Math homework? (He is 8!)

I've attached a photo of it.

The Easy and Speedy part is fine.

However "Some subtracting" is weird - those middle numbers crossed out are on the original sheet. I can't figure out how they work. The subtractions themselves obviously work if you just ignore the crossed out numbers, and adjust for hundreds, tens and units, but why are the crossed out numbers there in the first place? They must be some sort of working out, but what? I come up with a rule that explains some of them but I can't explain them all.

Then finally there is 12, 13 and 14: "Choose three numbers to create a 3-digit number. Re-arrange the digits and subtract the smaller number from the larger number. Do this three times". This doesn't seem to me very clear. Is this what they are looking for:

Choose three numbers: 1 8 6
Re-arrange the digits and subtract the smaller number from the larger number: 8 - 6 - 1 = 1

Do this three times - just choose three numbers another two times?
Choose three numbers: 3 9 2
rearrange and subtract: 9 - 3 - 2 = 4

Choose three numbers: 3 8 2
rearrange and subtract: 8 - 3 - 2 = 3

But since these follow from 9, 10 and 11 perhaps the three numbers are similar to those? But I don't see how?

Anyway here are the original questions:
I'd like to use Photoshop to be able to construct Floor Plans for home building.

In my initial research I noticed the Measurement Scale option that is an inches to pixels conversion. This seems to work well, but isn't quite accomplishing what I want:

I'd like to set this up for Inches to Feet, such that 1/4" is equal to 1' for the sake of accuracy. So, a quarter-inch on the screen (presumably Greyscale at 300dpi) is equal to a foot in real life.

I appreciate your assistance as it turns out that yes, I do indeed need to do math for this.

I want to know how does the body processes oils that we eat.
Does the oil gets stored in the body ?
Or does it get expelled.
Is there any good video explaining it ?
And good site or anything which shows the link between food and its processing and how good food effects the body and how bad food destroys it.
What makes junk food bad why does it cause diseases etc etc ?

STEM education is growing rapidly and preparing the next generation to fulfill the needs of our society's technology demands.  

In what ways has EE helped you continually learn, even as professionals?
How can EE support STEM as a great learning resource?
I have an image which is 320x240 px

I have an array of values for each pixel in the image (76,800 points)

If the user hovers over any part of the image I need to look at the array and return the corresponding value for it.

X Y position [0,0] of the image = the first value in the array.

If I wanted to find out the X Y position [65,33] of the image, and then look up the  value in the array, what would be the correct forumla to do this
Well I was revising how 'magnetic' force is created and I came up to an issue?

Why do we measure only the charge net density only from a frame reference that electrons dont move?
I recently drove my car into the outside of my house and the circa 1860 plaster fell off the inside wall due to the impact.

The house is still structurally sound but the plaster that fell off the inside wall really smells bad. What is creating that horrible smell and how can I get rid of it?
We have a reference system in a conducting coil . Our reference velocity is the velocity of current(electrons).

Why the spacing between the nuclei is smaller than if we take as reference system with reference velocity the velocity of nuclei?

Length contraction decreases the dimensions of the nuclei , not making smaller the spacing between the nuclei.
Are LED's forward voltage dependent on the type of the semiconductor?

For example if a Led emmits red light is its forward different from a LED that emmits blue light?
Hello and Good Morning Everyone,

           I am wondering why C14 (subscript) would be used in a disinfectant/virucide.  I always thought that it a radioactive substance used in carbon dating of very old materials by archeologists and nothing else.   If used in a day to day disinfectant/virucide, could it be considered potentially carcinogenic to humans?

           Any feedback given to this question will be appreciated.

           Thank you

Why when I increase the  base resistor  the VCE voltage drop dicreases?
Hello and Good Evening Everyone,

        From a label on a disinfectant viricide bottle, I noticed an area listed as Inert Ingredients with a percentage of 99.93%.  Didecyl dimethyl ammonium chloride being  .04% and dimethyl benzyl ammonium chloride being  .03%.  Given this information, I am wondering what is meant by Inert Ingredients.  

         Any clarification which can be given for the meaning of Inert Ingredients will be greatly appreciated.  

         Thank you

Attached is Matlab command to convert polar form to rectangular form.  I'm converting 2e^j(pi/2) to rectangular form.

I was expecting real part to be 0 but it's a very small number.  Is this because there isn't enough bits to represent 0?
Nonstop train leaves Toronto and Montreal at the same time each day going to the other city along the main line. One trai travels at 120km/h and the other at 90km/h. Assuming the train is straight, how apart are they one hour before they meet?

The distance between Toronto ans Sudbury is 418 km. Terry leaves Sudbury on his motorcycle and went 105 km towards Toronto. Damon left Toronto at the same time on his motorcycle and drove 215 km towards Sudbury. How apart are Terry and Damon ?

Be a power thinker and solve this number puzzle by finding the correct values for A and B. The pictures are important

      A - B = 2                                  A(A in square) + 2 = B(B in cube)
For a number sequence A: (1, 2, 3, 4, 5, 6, 7, 8, 9, 10)

Are the terms in the subset B: (1, 4, 7, 8) considered in sequence given that some numbers from A were skipped?

Should I use the adjective sequential or succedent, or is there a better word?
Micheal has 16.25 $ in the bank. He needs 108 $ to buy a video game. He finds he can save 1.75 $ a week from his allowance. How many weeks must he save in order to have enough to buy the game.
Jenny has pennies , nickels , dimes , quarters , half dollars and/or dollar in her purse. still shes unable to make change for aa old two dollar bill.what is the greatsest amount of money she could possibly have.(She may have none of some of the coins.)

Barb has five small chains of three links each. She wants to make them into one long chain of 15 links. If cutting a link costs 20 cents and wedling a link costs 1.50$ what is the least cost of making the chain (Hint: You can do it for less than 6.80$.

Stefan is working on his garden. All of the flowers in the garden were white expect two,all are red except two and all are yellow except two. How many flowers are in stefan's garden.

in how many ways can change be made for for 85 cents using nothing but but nickels and/or dimes

I never tire of asking me: To be a good programmer, what is the relevance of getting a degree in computer science? And a good programmer has in mind all the commands of a programming language, like PHP or JAVA? The oldest languages (MSDOS) had less than 200 commands and functions, currently they must have more than 1000

I would like to hearing from you

Consider a binomial random variable X ~ Bi(n,∅).

We can get P(x) and P(x+1) as below but how to solve question 1 & 2 ?

P(x) = nCx . ∅ x (1- ∅)n-x
p(x+1) = nC x+1 . ∅ x-1 (1- ∅) n- (x+1)