An unconfined compression test was performed to determine the average strength of concrete cylinders (in psi). It is believed that the strength is approximately normally distributed with a standard deviation of 256 psi. A sample of 70 concrete cylinders was taken, and it was found that the average strength was 3000 psi. Find a 91% confidence interval for the true average strength of the concrete. Be sure to:

• State the value for α.
• State whether you should use z or t and find the appropriate value. Round z-values to 2 decimals. Round t-values to 3 decimals.
• Find the confidence interval (to 2 decimals). State the parameter your confidence interval is for.
• Write a verbal interpretation of your confidence interval.

Explained below.

Step-by-step explanation:

(1)

The confidence level is, 91%.

Compute the value of α as follows:

(2)

As the population standard deviation is provided, i.e. σ = 256 psi, the z value would be appropriate.

The z value for α = 0.09 is,

z = 1.69

(3)

Compute the 91% confidence interval as follows:

(4)

The 91% confidence interval for population mean implies that there is a 0.91 probability that the true value of the mean is included in the interval, (2942.29, 3057.71) psi.

the answer is a

step-by-step explanation:

39.00 x 24 = total installment price

carrying installment price - cash price

needed to save the .00/

step-by-step explanation:

12: 00 p.m. to 7: 00 p.m. is a total of 7 hours.

4: 00 p.m. to 7: 00 p.m. is a total of 3 hours.

this means that from 4: 00 p.m to 7: 00 p.m. this represents 3/7 of what was lost from 12: 00 p.m. to 7: 00 p.m.

after knowing this, after doing 11,600 - 6,800 = 4,800

4,800 represents 3/7 of what was lost for 7 hours.

we then divide 4,800 by 3 which gets 1,600.

because we know that 1,600 represents 1/7 of how much water was lost, we just have to multiply by 7, which gets 11,200.   after adding 11,200 to how much water was left at 7: 00 p.m. which was 6,800. 11,200 + 6,800 = 18,000

this means that the pool originally had 18,000 gallons in the pool.

you can also check your work by doing 18,000 - 4(1600), which becomes           1800 - 6400 which gets you 11,600.