# combining

1. ### combining advective reactive transport equation for two solutes

This is a rather basic one sorry, but I am rather stuck.... all I want to do is apply the chain rule to combine the advective transport equation for two solutes such that dCa/dt =\nabla \cdot (D \nabla Ca)-v \cdot \nabla Ca + \sum Ja and dCb/dt =\nabla \cdot (D \nabla Cb)-v \cdot \nabla Cb +...
2. ### Combining sums problem

The problem statement, all variables and given/known data I'm having some confusion about combining sums. Our goal when combining these sums is to have the, (x-c)^{\text{whatever}} term to be the same in both sums. My confusion is better explained in an example. (see below) The attempt...
3. ### Combining normal random variable question

I am stuck on this question... I know for part a) that E(X-Y) = -1 and Var(X-Y) = 5, but I'm not sure where to go from here... Is X-Y still a normal random variable? If so then I get Norm(-1,5) but I don't know where to go from there either. For part b) I don't understand what the...
4. ### Reference for combining correlated estimates with unequal variances

Hello, I am attempting to understand the theory behind combining correlated estimates which have unequal variances. All the estimates are unbiased estimates of one true mean. I've been reading the paper "Almost linearly-optimum combination of unbiased estimates" by Max Halperin. (If my...
5. ### Combining Multiple Binomial (or Negative Binomial) Distributions

I have been struggling with a problem, and am seeking help on the topic: I have two dice, one with a faces and the other with b faces. Only one success can come from each die, such that the success rates of the dice are 1/a and 1/b. I want to know the expected number of times I must throw...
6. ### combining binomial & normal distribution

if 4 items are chosen at random, what is the probability that their average length is greater than 35cm. mean = 35.05cm std dev = 0.2 i know that the probability of 1 item greater than 35cm is 0.5987 but unsure how to include 4 items and find mean? maybe binomial?
7. ### Combining two equations by addition or multiplication?

Hello all, I have a seemingly simple question concerning the combination of two quadratic equations: z(x) = x^2 + 2*x - 1 z(y) = 2*y^2 + 3*y + 1 What is the significance of combining these two equations by multiplying them together versus simply adding them together? I know if I...
8. ### Combining Algebra Fractions Frustration...

I've been working through an Algebra book trying to re-teach myself...not doing a half-bad job. I've come to a problem I'm not sure I understand. I reach the right answer...but yet it's wrong. I've attached the problem, along with the way I've been working it into a MS Word doc file. Any insight...
9. ### Combining differientation rules.. (chain, product, quotient)

I know all 3 of the rules (product, chain, quotient) and I know how to apply them to derive a function when that function ONLY uses 1 of those rules. But questions like this confuse me: y = [ (2x-1)^2 ] / [ (x-2)^3 ] Sorry if my brackets look a bit weird i'm trying to make the question...
10. ### combining logs

Express the given quantity as a single logarithm. ln(a + b) + ln(a - b) - 9 ln(c) Here is what I did: ln a + ln b + ln a - ln b - 9 ln c The ln b's cancel. ln a + ln a - 9 ln c Then combine to one logarithm. ln(a^2 - c^9) The outcome I got was incorrect. I was just wondering if you could...
11. ### Combining skills : Simplyfing Expressions.

Explain how it solved?
12. ### Thinking question for trig + combining functions

Hi, here's a really tough thinking question that has me totally stumped. Could someone please show me how to approach it? Determine a sine function, F, and a cosine function, G, such that y= (squareroot of 2)sin(pi(x-2.25)) can be written in the form of F-G. The solution at the back is: f(x)...
13. ### Combining 2 Functions

Hi, can someone help me with this question: The fuction P(t) = 5000-1000cos((pi/6)t) models the deer population in a provincial park. A disease in the deer population has caused it to decline. Biologists have discovered that the deer population is decreasing by 25 deer each month. a) Assuming...
14. ### combining confidence intervals

Suppose I have the regression Y=X_1 \beta_1 + X_2 \beta_2 +X_3 \beta_3 + X_4 \beta_4+U Where each X is an n-vector and each beta is a scalar. Unde the usual assumptions for OLS, Step by step, how can I construct a 95% CI for \beta_1+\beta_3
15. ### Combining like terms?

This is for a physics question, but I figured since it was math-based, I might be able to post it here. The problem that I'm having is combining like terms - I know it's simple but for some reason I've forgotten. Here's my problem: I solved it up until here. Now I'm stuck. C = (3.69i +...
16. ### combining vectors

if a=<1,-1,2> b=<3,2,1> and c=<3,1> is it possible to add (a+c) or |a|+ |c| ? is it possible to do: (a dot a) x b ?
17. ### Combining fractions

How would you simplify this into one fraction? \frac{1}{x+1}-\frac{3}{2}
18. ### combining functions

A gas tank on a dock has a small puncture and is leaking gas at the rate of 1cm^3/min into a lake. It forms a circular slick that is 1 mm thick on the surface of the water. Find the amount of gas leaked as a function of time?
19. ### combining functions

f(x)=3^x g(x)=x+2 h(x)=2x-3 which i need to arrange to get y=\frac{1}{27}*3^{2x}+2 i can get the last part of the equation when i do g*f(x+3)*h(x) but not sure where the fraction comes from
20. ### Combining Functions- Word Problem

I am having trouble with a word problem.. I am not very good at translating these into a formula. "73) A bicycle has two sets of gears, one at the pedals and one at the rear wheel. A typical 10-speed bicycle has two gears on the chain wheel and five hears on the rear wheel. The speed at which a...