21)If the random variable, x, is normally distributed, percent of all possible observed values of x will be within two standard deviations of the mean.

the 3rd option is right

step-by-step explanation:

i think is 3 and 6. this took me 10 min to think.hope to and hope that my answer is brainliest.(follow me )

step-by-step explanation:

we have

using a graphing tool

see the attached figure

this is a quadratic equation (vertical parabola) open up

the vertex is a > vertex

the domain of the function is all real > interval (-∞,∞)

the range of the function is the > [-6.125,∞)

the function has two x->   and

the function is increasing over the > (0.25,∞)

the function is decreasing over the > (-∞,0.25)