<!--- Filename should be: topic_story_anwserformat.Rmd --->
<!--- vm_poExp_8_1a.Rnw --->
  
```{r,  echo = FALSE, results = "hide"}
library("exams")
include_supplement('exponential.num', recursive=TRUE)
library("exams.forge")
instruction <- NULL
library("extraDistr")
rateperhour <- sample(10:25, 1)
rate    <- rateperhour/60
sec     <- 60/rate
d       <- distribution("exp", rate=rate)
ptype   <- "variance"
border  <- 0
lsg     <- 1/(d$rate^2)
number  <- rateperhour
length  <- 60
lambda  <- rate
rvt     <- rv("T", "Wartezeit in Minuten auf den nächsten Wähler")
sc      <- num_result(lsg, 3)
```

Question
========

```{r, error=TRUE, child=instruction}
```

In ein Wahllokal kommen durchschnittlich `r rateperhour` Wähler pro Stunde. Berechnen Sie die Varianz für die Zufallsvariable `r rvt`. 

```{r, child='exponential.num'}
```

Meta-information
================
extype: num
exsolution: `r sc$fx[1]`
extol: `r sc$tolerance`
exname: `r knitr::current_input()`
