Question

A filling machine puts an average of four ounces of coffee in jars, with a standard deviation of 0.25 ounces. Forty jars filled by this machine are selected at random. What is the probability that the mean amount per jar filled in the samped jars is less than 3.9 ounces?

Answer 1

Solution :

Given that ,

mean = = 4

standard deviation = = 0.25

n = 40

= 4 and

= / n = 0.25 / 40  

P( < 3.9) = P(( - ) / < (3.9 - 4) / 0.25 / 40  )

= P(z < -2.53)

Using standard normal table,

P( < 3.9) = 0.0057

Probability = 0.0057