Question

Thompson and Thompson is a steel bolts manufacturing company. Their current steel bolts have a mean diameter of 141 millimeters, and a standard deviation of 7. If a random sample of 39 steel bolts is selected, what is the probability that the sample mean would be greater than 141.4 millimeters

Answer 1

Answer:

Probability that the sample mean would be greater than 141.4 millimetres is 0.3594.

Step-by-step explanation:

We are given that Thompson and Thompson is a steel bolts manufacturing company. Their current steel bolts have a mean diameter of 141 millimetres, and a standard deviation of 7.

A random sample of 39 steel bolts is selected.

Let $\bar X$ = sample mean diameter

The z score probability distribution for sample mean is given by;

                            Z  =  $\frac{ \bar X-\mu}{\frac{\sigma}{\sqrt{n} } } }$  ~ N(0,1)

where, $\mu$ = population mean diameter = 141 millimetres

           $\sigma$ = standard deviation = 7 millimetres

           n = sample of steel bolts = 39

Now, Percentage the sample mean would be greater than 141.4 millimetres is given by = P($\bar X$ > 141.4 millimetres)

      P($\bar X$ > 141.4) = P( $\frac{ \bar X-\mu}{\frac{\sigma}{\sqrt{n} } } }$ > $\frac{141.4-141}{\frac{7}{\sqrt{39} } } }$ ) = P(Z > 0.36) = 1 - P(Z $\leq$ 0.36)

                                                            = 1 - 0.6406 = 0.3594

The above probability is calculated by looking at the value of x = 0.36 in the z table which has an area of 0.6406.