Answer:
a
[tex]P(X < 24 )= 21.186\% [/tex]
b
[tex]x = 19.78 \ months[/tex]
Step-by-step explanation:
From the question we are told that
The mean is [tex]\mu = 26 \ months[/tex]
The standard deviation is [tex]\sigma = 4 \ months[/tex]
Generally 2 year is equal to 24 months
Generally the percentage of total production will the company expect to replace is mathematically represented as
[tex]P(X < 24 )= P(\frac{X - \mu }{ \sigma} < \frac{24 - 26}{4} )[/tex]
Generally [tex]\frac{X - \mu}{\sigma } =Z (The \ standardized \ value \ of \ X )[/tex]
[tex]P(X < 24 )= P(Z < -0.8 )[/tex]
Generally from the z-table
[tex]P(Z < -0.8) = 0.21186[/tex]
So
[tex]P(X < 24 )= 0.21186[/tex]
Converting to percentage
[tex]P(X < 24 )= 0.21186 * 100[/tex]
=> [tex]P(X < 24 )= 21.186\% [/tex]
Generally the duration that should be the guarantee period if Accrotime does not want to make refunds on more than 6% is mathematically evaluated as
[tex]P(X < x) = P(\frac{X - \mu }{\sigma} < \frac{x - 26}{4} )= 0.06[/tex]
=> [tex]P(X < x) = P(Z < \frac{x - 26}{4} )= 0.06[/tex]
From the normal distribution table the z-score for 0.06 at the lower tail is
[tex]z = -1.555[/tex]
So
[tex]\frac{x - 26}{4} = -1.555[/tex]
=> [tex]x = 19.78 \ months[/tex]
