Question

The average price for an oil change is 35$ . In random sample of 20 oil changes, find the probability that the mean cost exceeds 42$ given that the population standard deviation is 87$. Please draw everything out so I can understand

Answer 1

Solution :

Given that ,

mean = = $35

standard deviation = = $87

n = 20

= 35

= / n = 87/ 20 = 19.4538

P( >$42 ) = 1 - P( <$42 )

= 1 - P[( - ) / < (42 - 35) /19.4538 ]

= 1 - P(z <0.36 )

Using z table,    

= 1 - 0.6406

= 0.3594