Question 1207570
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You can use a specialized Z calculator as the other tutor mentions. 
I'll use a Z table.


First we need to compute the z score.
z = (x - mu)/sigma
z = (252 - 266)/17
z = -0.82 approximately
I'm rounding to two decimal places because it is standard for many Z tables.


Such tables can be found in the back of your stats textbook.
If you don't have your textbook with you, then you can use an online resource such as this
<a href="https://www.ztable.net/">https://www.ztable.net/</a>


Let me know if you have questions on how to read the table.


Using such a table will determine that
P(Z < -0.82) = 0.20611
and then that leads to this
P(Z > -0.82) = 1-P(Z < -0.82)
P(Z > -0.82) = 1-0.20611
P(Z > -0.82) = 0.79389
Each decimal value mentioned is approximate.


That translates back to P(X > 252) = 0.79389 approximately when the mean is mu = 266 and the standard deviation is sigma = 17.


The percentage of pregnancies that last beyond 252 days is <font color=red>approximately 79.389%</font> depending how you round it.


This accuracy can be improved through the use of a specialized Z calculator. 
Some teachers will allow specialized Z calculators; while other teachers will only allow a stats table and standard calculator.
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