help

yes i should have done that, sorry for this i was just very frustrated and
could not solve it. I guess i only needed hint for commands and not the
solution. I will think a bit more and maybe
i get back too you with a more well formulated question.
I think this is a very good site and you are doing a fantastic job.
cheers
Lotta






15 maj 2012 kl. 16:24 skrev Sarah Goslee:

Lotta,

If this isn't homework, then you need to read the posting guide (see
link at bottom of each posting to the list), and ask a more specific
question than "can't get any further."

What have you tried? What didn't work? Where did it go wrong? What
book are you working from? Etc. Even if not an ethics violation, your
question is too vague to be easily answered unless you can find
someone interested in working the entire problem from scratch. Since
we're all busy volunteers, that's unlikely. You need to do the work of
asking a well-formed question before you can expect much help.

Sarah

On Tue, May 15, 2012 at 10:10 AM, Eva-Lotta Blom
<eva-lotta.blom at bioenv.gu.se> wrote:

Hello Sarah

this is not a homework, i am trying to understand R by doing some exercise

in my book.

I will however participate a course in R in august and thought it could be

good to have some

knowledge before. I hoped for help from you since i have no instructor to

ask, that would have been

my first choice.

Ill look for help somewhere else then.

thanks anyway

Lotta










15 maj 2012 kl. 15:58 skrev Sarah Goslee:


Hi,


R-help is not a homework help list. If you're having trouble, you need

to speak with your instructor instead.


Best of luck,

Sarah



On Tue, May 15, 2012 at 8:04 AM, Eva-Lotta Blom

<eva-lotta.blom at bioenv.gu.se> wrote:



?1. ?Emma is performing an experiment that requires individual handling of

some animals. The sizes of the animals are lognormally distributed: The

natural logarithms of their sizes has a normal distribution with mean 3 and

standard deviation 0.4. The time (in minutes) it takes to handle each animal

is given by



10 + s ? 1.5 + e? for animals with s ? 20 20 + s ? 0.8 + e? for animals with

s > 20



where ? is a random variable that is normally distributed with expectation 1

and variance 0.3.



For a randomly picked animal, what is the (approximate) probability that it

can be handled in less than 30 minutes?



We can solve this exercise using simulation, as follows: Simulate a vector S

with the sizes of 10000 animals, by using the rnorm function and the ?exp?

function. Then, compute a vector Time of length 10000 with the times it

takes to handle each of these 10000 animals: Remember that to separate

between the two cases, you can use notation like for example ?Time[S < 20]?.

The random component e? can be added by combining the ?exp? function with

the ?rnorm? function. Finally, you can find the proportion of simulated

values below 30. Re-do the computations a couple of times to get an idea of

the variability of the result.



s <- c(10000)


S <- exp(rnorm(s, 3, 0.4)) [1]# vector 10000, mean, sd


Time <- 10+S*1.5 [1] # 10 + s ? 1.5 + e? for animals with s ? 20


time <- 20+S*0.8 [1] # ? 20 + s ? 0.8 + e? for animals with s > 20



can't get any further and i can't really find a good help page to solve the

code.


can you help me?


Lotta