Question

The following TI-84 Plus display presents some population parameters.

1-Var-Stats

x=146

Σx=2680

Σx2=359,620

Sx=3.92662001

σx=4

↓n=20

(a) Assume the population is bell-shaped. Approximately what percentage of the population values are between 142 and 150?

Answer 1

P (   142   < X <   150   )
=P( (142-146)/4 < (X-µ)/σ < (150-146)/4 )              
              
P (    -1.000   < Z <    1.000   )

= P ( Z <    1.000   ) - P ( Z <   -1.00   ) =    0.8413   -    0.1587   =    0.6827 or 68% (answer)