Question

a set of data has a normal distribution with a mean of 120 and a standard deviation of 10. Find the interval about the mean within 90% of the data lie

Answer 1

since the mean is 50% of the data, and 90/2 = 45

you want z values that correspond to 50-45 and 50+45

Answer 2

i take it that made perfect sense :)

Answer 3

z1 = -1.645

z2 = 1.645

\[z_n=\frac{x-mean}{sd}\]
\[z_n(sd)+mean=x\]
\[\pm1.645(10+120)=x_1,x_2\]

Answer 4

latex fail :)

\[\pm1.645(10)+120=x_1,x_2\]

Answer 5

so the choices are:
94.2-145.8
103.5-136.5
113.68-126.32
100.4-139.6

Answer 6

so about, 120 - 16 and 120 + 16

Answer 7

ohh thanks!