7. The heights (in inches) of adult males in the United States are believed to be Normally distributed with mean . The average height of a random sample of 25 American adult males is found to be x= 69.72
inches, and the standard deviation of the 25 heights is found to be s=4.15 A 90% confidence interval
for

Step-by-step explanation:

Information given

represent the sample mean

population mean (variable of interest)

s=4.15 represent the sample standard deviation

n=25 represent the sample size  

Confidence interval

The confidence interval for the mean is given by the following formula:

  (1)

The degrees of freedom, given by:

Since the Confidence is 0.90 or 90%, the significance is and , and the critical value is

Now we have everything in order to replace into formula (1):

He should row at the speed of 12 kilometers per hour.

Step-by-step explanation:

Given:

An athlete plans to row upstream a distance of 6 kilometers and then return to his starting point in a total time of 4 hours.

The rate of current is 2 km/hr.

Now, to find how fast should he row.

Let speed of the athlete row be .

Distance = 6 kilometres.

So, to get the time of upstream:

Rate of upstream = .

Time of upstream =

Now, to get the time of downstream:

Rate of upstream=

Time of downstream = .

Now, as given total time 4 hours.

Thus, we set an equation:

Time of upstream + time of downstream = total time.

Multiplying both sides by 6 we get:

Dividing both sides by 2 we get:

Therefore, he should row at the speed of 12 kilometers per hour.