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The modulus of a complex number 2016-07-29
From Cheyenne:
There's a question on my Summer Assignment I cant figure out. Here it is:

Find the absolute Value of the complex number. -5i

Calendar arithmetic 2016-02-14
From Jenalee:
January 1, 2001 is Julian Day 2 451 911 (the number of days that have passed since Day 0, January 1, 4713 BC).

If Julian Day 0 was a Monday, what day of the week was January 1, 2001?

A model of the sun and the Earth 2014-06-14
From Lynn:
There is a model of the sun that is 2 1/2 inches in diameter. This is the only clue we have! How far away is the earth from this model?
What is the value of |2((i)^(1/2))|? 2013-07-22
From Delilah:
What is the value of |2((i)^(1/2))| ?
i.e. absolute value of 2 multiplied by square root of i.

Mod versus Rem in Turing 2013-01-01
From Eric:
I am a teacher teaching computer science using Turing. I am having difficulty understanding why one would use the mod operator versus the rem remainder operator.

Mod seems to make the resulting sign depend on the sign of the divisor, whereas rem makes the resulting sign depend on the dividend.

Examples:

11 mod 5 = 1 and 11 rem 5 =1
-11 mod 5 = 4 and -11 rem 5 = -1
11 mod -5 = -4 and 11 rem -5 =1
-11 mod -5 = -1 and -11 rem -5 = -1

What I can't understand is why this would matter. For example, -11 / 5 = -2.2 and 11 / -5 = -2.2 get the same result.
So how is a remainder dependent on the sign of one of the parts? What benefit would using one over the other have?

Any insight would be most helpful!

Eric

The spread of a rumor 2012-04-09
From Roohi:
The function f(t) = a/(1+3e^(-bt)) has also been used to model the spread of a rumor. Suppose that a= 70 and b=3 0.2. Compute f(2), the percentage of the population that has heard the rumor after 2 hours. Compute f'(2) and describe what it represents. Compute lim t approaches infinity and describe what it represents.
Modular arithmetic 2011-10-30
From Kim:
Hello,
I am editing a resource for students, and I think some of the answers may be incorrect. The text I was given and my questions are in the attachment. Any help you could give would be appreciated.
Thanks,

Kim

Sales as a function of advertising 2010-12-08
The sales S(in thousands if units) of a product after x hundred dollars is spent on advertising is given by S=10(1-e^kx). Find S as a function of x if 2500 units are sold when \$500 is spent on advertising.
(x^3 + 11x) is divisible by 6 2010-06-24
From PT:
Given that x is a non-zero integer, how do you show that for all values of x, (x3 + 11x) is divisible by 6?

I know it works but how do I answer the "all values of x" part?

A linear relationship 2010-06-22
From Laura:
The monthly cost of driving a car depends on the number of miles driven. Lynn found that in May it cost her \$300 to drive 480 miles and in June it cost her \$460 to drive 800 miles.

Question: Express the monthly cost C as a function of the distance driven d, assuming that a linear relationship gives a suitable model.

A scale model of a city 2010-05-18
From Briana:
Well I have to create a three dimensional city for a geometry project and it requires us to use precise scal factor and well we want to build a medium sized city but our teacher said that If we make or buildings to high our houses would look like super small compared to the tall building were trying to figure out if we were to build a medium sized city what scale factor should we use to make the houses big enough to see and design?
Answered by Walter Whiteley and Tyler Wood.
Modelling an underpass 2010-05-11
From Sue:
An engineer at the Ministry of Transport is creating the plans for a new road. This road will cross the path of a busy railway track so it will be necessary to built an underpass for this road. This underpass will be in the shape of a parabolic arch.

The specifications include:
-the road must be at least 10 m wide and it must have shoulders at least 2 m wide on either side of the road.
-there must be a clearance of 3 m over all areas of the road.

What quadratic equation could you use to model this bridge.

A model for the population of a Canadian city 2010-04-07
From jess:
Let t^2 represent t-squared. The population of a Canadian City is modelled by: f(t) = 12t^2 + 800t + 40,000, where t is the time in years. When t= 0, the year is 2007.
a) According to the model, what will the population be in 2010?
B) In what year is the population predicted to be 300,000?

A linear relationship 2010-02-24
From Mel:
This table shows the linear relationship between an aeroplane's height (above sea level) and the outside air temperature.
 h (cm) 120 340 480 600 1040 T (degrees C) 14.28 12.96 12.12 11.4 8.76
Find the gradient and vertical intercept of the function. Write the formula for T.

A 3D cardboard cupcake 2010-01-30
From Margaret:
Hi,
I'm an art student and I'm attempting to build a 3D cupcake out of cardboard. I want it to have a circular base of 8.5 inches and sides that are 7'' tall and slope outward so the top of the base is 29'. The top with the frosting would be a detachable lid made from a cone with a base circumfrance of 29". My problem is how to cut the side so they will slope out, I'm pretty sure there needs to be a curve, however I don't how to calculate the degree of it. Ideally I want the sides to be a single piece of cardboard. I also don't know how to calculate the arc needed to make a cone who's circular base's circumfrence is 29''.
Thanks,
Margaret

Commodity price increase 2009-11-04
From bharat:
if price of a commodity increases by x% the to keep the expenditure same the decrease in consumption should be (x/(x+100))*100, why?
Constructing a scale model 2009-09-27
From Colleen:
What is the formula i need to use to find out how to state a reasonable scale in the question below; Suppose you were constructing a model that must sit on a piece of cardboard that is 22cm by 28cm. STATE THE REASONABLE SCALE that you can use to build a model to represent the following items. Determine the dimensions of the model.

a) a rectangular prism with a length of 5m and a width of 2m?

Fitting the curve y=a*exp(b*x)+c 2009-08-12
From aika:
Could one show me the complete algorithm and formula for finding the coefficients (a,b, and c) in exponential regression model y=a*exp(b*x)+c
Math in everyday life 2009-08-03
From Naveen:
Dear sir, We are advised to do a project on "Mathematical modeling to solve various problems of our everyday life/environmental related problems...... Can u plz help us by mailng some ideas, suggestion,reference to make my project successful.... Thanking you...... Waiting for your favourable reply......
The scale for a model train 2009-03-13
From Shelly:
Lindy is planning to build a model of a train using a scale where 2 inches represents 25ft. If the train is 60 feet long, what is the length in inches that Lindy should build the model of the train?
Answered by Stephen La Rocque and Penny Nom.
Two modular equations 2008-10-08
From Mhiko:
please solve this Chinese remainder problem..and give me a solution or rule in order to solve this problem/

x=2mod15
x=1mod25

Remainders 2008-06-30
From vivek:
what is the remainder when 2050*2071*2095 is divided by 23 ? this question needs to be done in as less time as possible.
The mean, the median and the mode 2008-06-23
From Crystal:
Hi my name is Crystal,
My question is
under what circumstances will the mean, the median, and the mode all have the same value?

Answered by Stephen La Rocque and Harley Weston.
A linear model 2008-05-09
From Shelby:
How would you write a linear model to represent the population of a city that has a population of 547,725 and a growth rate of -25,195 per year with t represents the number of years since 1994?
A complex number in polar form 2007-07-23
From roland:
write the given complex number z in polar form lzl(p+qi) where lp + qil=1 for 3 - 4i.
A model for a building 2007-07-17
From Carl:
A model for a building is 50 centimeters long, 38 centimeters wide, and 225 centimeters tall on model 1 centimeter represents 2.5 meters. I need to find the volume of the actual building in cubic meters,and the surface area of the building including ceilings and floors. round to the nearest tenth of a square meter.
The "mode" of a set of numbers 2007-06-06
From Anthony's mom:
we have a graph: Kindergarten has 1, 1st has 5, 2nd has 4, 3rd has 3
is the mode "1st grade" because there are more children in that grade?

Using a stem and leaf plot 2007-05-22
From Maegan:
The students in Mr.Smiths PE class collected data on the number of sit ups the students were able to do in three minutes. Use the data to create a stem and leaf plot. What is the median for the class data? range? mode?
Can you have median < mode < mean? 2007-04-11
From Kaliela:
Can the Median > mode > mean?
Can the Mean > Mode > Median?
I don't think either of these can occur but I'm unsure why?

A missing observation 2007-04-02
From destinee:
Exponential form of complex numbers 2007-02-12
From Austin:
When dealing with imaginary numbers in engineering, I am having trouble getting things into the exponential form. The equation is -1+i now I do know that re^(theta)i = r*cos(theta) + r*i*sin(theta). Just not quite understanding the order of operations. Thanks
A scale model 2006-11-30
1) A model of a storage compartment is to a scale of 1:40. If the surface area of the model is 25 square centimeters, what is the surface area of the actual storage compartment?

a) The storage compartment in the last question has an actual volume of 8 cubic metres. What is the volume of the model?

A scale factor 2006-03-25
From Jackie:
I need a formula or step by step help to show my child how to find missing dimensions for example: The scale factor for a model is 10 inches = ________ feet
Model 39.7 in
Actual 11.9 ft

A train model is created using a scale of 1:60 2006-01-01
From Jennifer:
An "n gauge " train model is created using a scale of 1:60. If an actual train engine, the "K-4" an early twentieth-century engine,is 45 feet long, what is the length of an "N gauge" model of the engine in inches?
The number is increased by the sum of its digits 2005-11-07
From Ernesto:
The number 1 is written on a blackboard. After each second the number on the blackboard is increased by the sum of its digits. is it possible that at some moment the number 123456 will be written on the blackboard?
Three prime numbers p,q and r, all greater than 3, form an arithmetic progression: 2005-07-18
Three prime numbers p,q and r, all greater than 3, form an arithmetic progression: p=p, q=p+d and r= p+2d. Prove that d is divisible by 6.
The sum of the digits of 2^100 2005-06-11
From Richard:
The sum of the digits was calculated for the number 2100, then the sum of the digits was calculated for the resulting number and so on, until a single digit is left.
Divisibility of a^2 + b^2 2005-05-16
From Ampa:
given natural numbers a and b such that a2+b2 is divisible by 21, prove that the same sum of squares is also divisible by 441.
Modelling monthly temperature with a cosine 2004-12-25
From Regis:
The average monthly temperature for a location in Ontario as a function of month number can be modelled using the equation y = a cos[k(t + b)] + d.
Two modes 2002-12-12
From ali:
I have a math assignment to pick the mode in a set of data. 12 and 21 both appear twice in the data set. What is the mode?
Mean, median and mode 2002-09-08
From Ramona:
1. How do you calculate the mean, median, and mode?

2. what are each of their definitions?

The Dugout, Don's Basement, Cd Corner,... 2002-04-30
From A student:
The Dugout, Don's Basement, Cd Corner, Harry's Deli, Bill's Software, Anne's Footwear, and Joanne's House cleaning.

The gift certificates are each in multiples of \$5. There is a \$100 range in the value of the gift certificates, which start at \$25. The mean value of all seven gift certificates is \$80, and the median and mode are both \$70.

The certificate from The Dugout is worth the most and the one from Joanne House cleaning is worth the least.

The total value of the gift certificates from CD Corner, Harry's Deli, and Anne's Footwear is \$270, but Anne's Footwear certificate is worth \$50 more than the one from Harry's Deli. The Cd Corner gift certificate is equivalent to the mean for this group of three.

What is the value of the gift certificates from each store?

Take It! 2002-04-03
From Bryan:
You are playing Take It! for \$180,00 with a total stranger. There are 180 identical balls in a big vase. Each player in his turn, reaches into the vase and pulls out 1,5,or8 balls. These balls are discarded. The player who takes the last ball from the vase wins the \$180,000. A flip of the coin determines that you will go first. Are you glad? How many will you take out on the first move, and how will you proceed to win the prize?
The best linear model 2001-07-29
From Rebeca:
I am a student (senior) summer hire working for Dept of the Army Resource Management. I've been assisting the Analyst in developing a model to predict training costs. The technique we used was simple linear regression. Now I've been asked for my opinion in choosing the best model I feel is better. I've chosen #1. Garrison Training but I want a second opinion before I give my choice. I've taken basic statistics last year in high school and will probably be taking more this year. Could you look over the information and give me a reason my choice would not be best? The dep variable-y, is Training costs in dolars per day.

ModelInd Variable- Xabrsy.x
1.Garrison Training126.310.9820.9055117.2
2.Local Training212.161.370.7937142.7
3.Man Rig Area116.382.470.6481175.6
4.Major Training346.124.670.7280167.2

Conservation, consumption and population growth 2001-06-04
From Steve:
I'm trying to quantify the relation between conservation/consumption and population growth. For instance let's consider California:

The 2000 census states that California's population grew from 29,760* in 4-1990 to 33,871 in 4-2000. I want to find r or rate of growth per year. Based on the exponential growth formula for population growth:
.
.
.

Toy bricks 2001-05-13
From Sarah:
A regular-sized brick weighs 4 kilograms. How much will a similar toy brick, made of the same material, but all of the same dimensions of which are four times smaller, weigh?

The 300-metre tall Eiffel tower is made of steel and weighs 8 000 000 kg. An exact replica, made of the same material, weighs 1 kg. How high is the replica

What is the difference between Mean and Average? 2000-12-13
From Julie:
What is the difference between Mean and Average? My thinking is the average, is the equal to the sum of all numbers divided by the number of numbers added together. But the mean, I think should be calculated by adding the largest and smallest numbers in the set and them dividing by 2. (which is the point where 1/2 the numbers are higher and 1/2 the numbers are lower)
Answered by Patrick Maidorn and Penny Nom.
Mode 2000-09-22
From James Barton:
I have always been told that a mode is the "one" number that appears most in the set of numbers: ex.{1,3,4,6,3,2} the mode is 3. What if you have {1,1,3,4,5,5}is there a mode. I was taught long ago that there is no mode, Not i am having to teach there is two modes. 1 and 5. If this is the case if we have {1,1,2,2,3,3,4,4,5,5} that every number is the mode. True or false. This is being ambigiuous if we say all are the mode. Because no one number is used more than the others.
Answered by Claue Tardif and Harley Weston.
Finding a formula 2000-05-05
From Erica Hildebrandt:
If a farmer has a field and his plots are laid out in the following grid where each # represents a plot:
 4 5 12 13 20 3 6 11 14 19 2 7 10 15 18 1 8 9 16 17

Of course the plot numbers aren't meaningful as I have described above. In fact they may not be numbers at all. The only constants I have are the total number of rows and columns. Using the total number of rows and columns and my current position row and column, how can I write a formula that tells me column 3 row 3 = 10, column 4 row 2 = 14, etc. I can see the pattern but can't quite get the formula. I believe I will need 2 different formulas one for even and one for odd rows.
Answered by Paul Betts and Penny Nom.

A model area 1999-12-15
From John Ost:
Hello, I am a college student taking an elementary math course I need if possible assistance to developing an area model 36 x 25 that shows each of the four separate partial products. I must know how to do the computation 36x25 showing each of the four partial products separately, and indicate how each corresponds to the drawing that is required of the area model.
Mean, median and mode 1999-12-07
From J William Morning:
Using the data values 2,2,10,6,5, determine the median, mode and mean.
Linear models 1999-11-09
From Helen Moreno:
What is a linear model?
Mean, median and mode 1999-11-06
From Rick:
I have five number places and the mean and median are both "0". The mode is greater than the mean. The sum of the absolute values of all of the numbers is 20. The smallest number is 4 less than the next smallest number. What are the five numbers. (negative integers can be used) All of the numbers are integers.
Divisibility by 9 1999-02-21
From Razzi:
I've been having a hard time trying to solve the following problem and I was wondering if you could help me.

For any positive integer a let S(a) be the sum of its digits. Prove that a is divisible by 9 if and only if there exist a positive integer b such that S(a)=S(b)=S(a+b).
Answered by Chris Fisher and Harley Weston.

Modular Arithmetic 1999-02-04
From Leslie Kupper:
I am trying to do a project on modular arithmetic. I was wondering if there were any websites that include a sample lesson plan on modular arithmetic for any grade level. Let me know where and how to find them. Thanks.
Absolute value of i 1999-01-06
From Wayne Bagley:
I would like to know what is the absolute value of i. I need an answer suitable for the secondary level.
A Logic Problem 1998-06-07
From Anthony Bacigalupo:
My name is Anthony Bacigalupo and I take Sequential ][ Math and am taking a practice regents. When doing a logic problem, I encountered the following statements, where I am trying to prove P ( I left out steps unrelated to the question)....
Clock Arithmetic. 1998-03-09
From Joann Dixon:
What is clock mathematics?
Arithmétique modulaire 2008-01-10
From hausknecht:
ma grand mère a entre 60 et 80 ans.il y a un an son âge était un multiple de 3.dans deux ans son âge sera un multiple de 2,de 3 et de 9.cette année , c'est un multiple de 5.quel est l'âge de ma grand mère?
mod n 2005-04-26
From Jean:
Réecrire (5A27)en base 16 changer en base 8 ( (2n)!+ 1) (mod n) (1-764n) (mod n) (n+1)exposant 78355 (mod n) PPCM(n!+1 , n!)