Answers

2014-10-18T05:33:47+05:30

This Is a Certified Answer

×
Certified answers contain reliable, trustworthy information vouched for by a hand-picked team of experts. Brainly has millions of high quality answers, all of them carefully moderated by our most trusted community members, but certified answers are the finest of the finest.
1)
X1 = 12      X2 = 26           μ = 20      σ = 80 or 8 ?       N = 80

Z1 = normal distribution variable = (X1 - μ) / σ = -0.1
Z2 = (X2 - μ)/σ = +0.075

Probability of a given case being X1 < X < X2 =  ZTable (-0.1 < Z < 0.075)
           = ZTable (0 < Z < 0.1) + ZTable (0 < Z < 0.075)
           = 0.03980 + 0.02989 = 0.06969

Percentage of cases = 6.969 %  or   nearly 7%
==============
2)
       X > 30 
      Z = (X - μ)/σ = 0.125
   ZTable (Z > 0.125) = 0.5 - ZTable (0<Z < 0.125) = 0.5 - 0.04974 = 0.45026

Number of persons with score X > 30 = 0.45026 * N = 36.0208 
Percentage of cases = 36.0208 * 100 / 80 = 45.026 %, same as probability * 100.


0