In: Statistics and Probability
A popular retail store knows that the purchase amounts by its customers is a random variable that follows a normal distribution with a mean of $30 and a standard deviation of $9. What is the probability that a randomly selected customer will spend between $20 and $35 at this store? Place your answer, rounded to 4 decimal places, in the blank. For example, 0.3456 would be a legitimate entry.
µ =    30      
           
           
σ =    9      
           
           
we need to calculate probability for ,  
           
           
       
20   ≤ X ≤    35      
           
       
X1 =    20   ,   X2 =  
35          
       
          
           
           
Z1 =   (X1 - µ ) / σ =   -1.111  
           
           
Z2 =   (X2 - µ ) / σ =   0.556  
           
           
          
           
           
P (   20   < X <   
35   ) =    P (   
-1.111111111   < Z <    0.556  
)
          
           
           
= P ( Z <    0.556   ) - P ( Z
<   -1.111   ) =   
0.7107   -    0.1333   =   
0.5775(answer)
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excel for probability from z score
=normsdist(z)