SD FOR MEAN !!!

Question

help
how can I solve this ?
We are working with the mtcars dataset and need to find the number of cars that fall into 1 standard deviation from the mean of the mpg column.
This means that we need to find the cars that have the mpg value in the range of mean(mpg)-sd(mpg) and mean(mpg)+sd(mpg).

Answer 1

# note the , ! x is a dataframe, not a vector!
x<- mtcars[mtcars$mpg<a &mtcars$mpg>b,]

# a x is a dataframe, you need to determine the number of rows, not the length
nrow(x)

Answer 2

You calculate the values and then filter the mpg column by them

Answer 3

a<-mean(mtcars$mpg)+sd(mtcars$mpg)
b<-mean(mtcars$mpg)-sd(mtcars$mpg)
x<- mtcars[mtcars$mpg<a &mtcars$mpg>b]
length(x)
why is this wrong please ?

Answer 4

thank you I get it

Answer 5

x <- (mtcars$mpg)
a<-mean(mtcars$mpg)-sd(mtcars$mpg)
b<-mean(mtcars$mpg)+sd(mtcars$mpg)

tar <- mtcars[mtcars$mpg>a & mtcars$mpg<b,]
print(nrow(tar))

Answer 6

mean1 <- mean(mtcars$mpg)
sd1 <- sd(mtcars$mpg)

lowr <- mean1 - sd1
uppr <- mean1 + sd1

in_range <- subset(mtcars, mpg >= lowr & mpg <= uppr, select= c(mpg))
print(length(in_range$mpg))