Assume that the helium porosity (in percentage) of coal samples taken from any particular seam is normally distributed with true standard deviation 0.76.(a) compute a 99% ci for the true average porosity of a certain seam if the average porosity for 16 specimens from the seam was 4.85. (give answers accurate to 2 decimal places.)

Step-by-step explanation:

Formula to calculate the confidence interval for population mean is given by :-

, where = sample mean

n= sample size.

z*= Critical value

= Population standard deviation.

As per given , we have

n= 16

From z-table , the critical value for 99% confidence = z*=2.576

Now , 99% confidence interval for true average porosity of a certain seam will be :

Hence, the required  99% CI for the true average porosity of a certain seam =

b. 1.25 hr

step-by-step explanation:

if you have a constant speed of 60 mph, then you have a ratio between 60 mi. to 1 hr. dividing both sides by 60 we get the ratio

1 mi. to

then mult. both sides by 75 we get the ratio

75 mi. to

simplifying we get

75 mi. to

or 1.25 hr.