Question

1. A population has a mean of 300 and a standard deviation of 18. A sample of 144 observations will be taken. The probability that the sample mean will be less than 303 is

1. 0.4332
2. 0.9772
3. 0.9544
4. 0.0668
5. None of the above

Answer 1

Solution :

Given that,

mean = = 300

standard deviation = = 18

n = 144

= 300

=  / n = 18/ 144=1.5

P( <303 ) = P[( - ) / < (303-300) /1.5 ]

= P(z <2 )

Using z table  

= 0.9772

probability= 0.9772