supposing the mean is 6.8 and standard deviation is 2.7, then the highest 1% and the lowest 1% of numbers in that population will be

Question

supposing the mean is 6.8 and standard deviation is 2.7, then the highest 1% and the lowest 1% of numbers in that population will be--------------(Choose one of these R functions to answer the question: dnorm(), pnorm(), qnorm(), rnorm()).

Answer 1

Ekene,

 

The R functions dnorm, pnorm, qnorm, and rnorm give you specific statistics values based on mean and standard deviation. The dnorm function gives you a density value (probability at that point), the pnorm gives you the cumulative probability, the qnorm function gives you a probability based on a percentile or range of percentiles, and rnorm gives you a random probability. In this case you're given two percentages, so use qnorm. The syntax is as follows:

qnorm(percentage, mean=μ, sd=σ)

 

The cool trick here is that if you're looking for multiple percentages, just use the c function:

qnorm(c(p1,p2,p3,etc),mean=μ, sd=σ)

 

So plug in your mean and standard deviation and your two percentages into the formula qnorm and you're all set! Hope that helps.