Question 933923
 H0: u = 39 
 Ha: u<39 
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Sample of 15 Statistics: mean of 38.8", standard deviation = 2 inches
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test stat: z = -.2/(2/sqrt(15)) = -.39 rounded
p(z < -.39) = .35 rounded
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significance level of 0.05. (critical value z = -1.64 rounded)
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.35 > .05
Do not reject Ho.
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For the normal distribution: Below:  z = 0, z = ± 1, z= ±2 , z= ±3 are plotted.  
.35 the Area under the standard normal curve to the left of z = -.39
Note: z = 0 (x value: the mean) 50% of the area under the curve is to the left and 50%  to the right
{{{drawing(400,200,-5,5,-.5,1.5, graph(400,200,-5,5,-.5,1.5, exp(-x^2/2)), green(line(1,0,1,exp(-1^2/2)),line(-1,0,-1,exp(-1^2/2))),green(line(2,0,2,exp(-2^2/2)),line(-2,0,-2,exp(-2^2/2))),green(line(3,0,3,exp(-3^2/2)),line(-3,0,-3,exp(-3^2/2))),green(line( 0,0, 0,exp(0^2/2))),locate(4.8,-.01,z),locate(4.8,.2,z))}}}