Ten consecutive strength tests are available for a new concrete mixture with fc= 4000 psi: 4830, 4980, 3840, 4370, 4410, 4890, 4450, 3970, 4780, and 4040psi a. Do the strength results represent concrete of satisfactory quality? Explain

b. If f'cr, has been selected based on 30 consecutive test results from an earlier project with a sample standard deviation Ss, of 570 psi, must the mixture proportions be adjusted? Explain.