Question

People of jupiter have a population mean IQ score of 120 with a population standard deviation of 24. You collect a random sample of 36 people of jupiter and figure their sample mean IQ score. Find a value so that the probability that the sample mean would fall above it would be 80%.

Answer 1

solution:

n = 36

= 120

= / n = 24 / 36=4

Using standard normal table,

P(Z > z) = 80%

= 1 - P(Z < z) = 0.80

= P(Z < z ) = 1 - 0.80

= P(Z < z ) = 0.20

z = -0.84 ( using z table)

Using z-score formula  

= z * +   

= -0.84* 4+120

= 116.64=117 rounded