Question

Problems 16-18: Lengths of pregnancies are normally distributed with a mean of 268 days and a standard deviation of 15 days.(Use the z-table). What percentage of pregnancies last less than 250 days?

What percentage of pregnancies last more than 280 days?

If 60 pregnant women were randomly selected, how likely is it that their mean pregnancy length is greater than 275 days? Your answer:

Answer 1

Solution :

Given that ,

mean = = 268

standard deviation = = 15

P(X<250 ) = P[(X- ) / < (250-268) / 15]

= P(z <-1.2 )

Using z table

=0.1151

answer=11.51%

(b)   

n = 60

= 268

= / n = 15 / 60 = 1.9365

P( >275 ) = 1 - P( <275 )

= 1 - P[( - ) / < (275 -268) / 1.9365 ]

= 1 - P(z <3.61 )

Using z table

= 1 - 0.9998

= 0.0002

probability= 0.0002