American Roulette standard error calculation


#1

# The variables 'green', 'black', and 'red' contain the number of pockets for each color
green <- 2
black <- 18
red <- 18

# Assign a variable `p_green` as the probability of the ball landing in a green pocket
p_green <- green / (green+black+red)

# Assign a variable `p_not_green` as the probability of the ball not landing in a green pocket
p_not_green <- 1-p_green

# Compute the standard error of the random variable

abs(17 - -1) * sqrt(p_green(p_not_green))    
#> Error in p_green(p_not_green): could not find function "p_green"

#2

What I am trying to do: The standard error of a random variable X tells us the difference between a random variable and its expected value. You calculated a random variable X in exercise 2 and the expected value of that random variable in exercise 3.

The output I desire: Now, compute the standard error of that random variable, which represents a single outcome after one spin of the roulette wheel.

The output I am getting : Error: could not find function "p_green". I understand the error, just not sure how to correct it. can someone hint me the correct syntax ? thanks


#3

Check out sqrt(p_green(p_not_green))
In the way you've written this, you are saying "put the object p_not_green into a function named p_green". That is, when you follow a name with parentheses, R usually assumes you are trying to call a function. That's why you get the error "Error in p_green(p_not_green): could not find function "p_green""

I think you probably want to be applying some operator to these two objects, e.g. (p_green + p_not_green).


Also just to note our homework policy: FAQ: Homework Policy
But I think asking for hints as to how best to resolve issues with your approach to solving a homework problem, as Paul does, is usually cool.