Compressive strength of concrete cubes made for testing purp

Compressive strength of concrete cubes (made for testing purpose) is assumed to follow a normal distribution with mean strength of 6,000 psi and standard deviation of 1.000 psi. Mean and standard deviation arc representative of the entire population. Consider a sample of (1) 20 cubs and (2) 60 cubes. For each sample estimate the probability that sample average and sample standard deviation fall within 10% of population mean and standard deviation.

Solution

probability

0.10*20 / 1000 = 0.002

0.10 * 20 / srqt (6000) = 0.0258

probability

0.10*60 / 1000 = 0.006

0.10 * 60 / srqt (6000) = 0.07746