The surveyor created three separate concrete mixes, each with a different proportion of cement, admixtures, and so on. Each mix got three samples, which were then subjected to compressive and tensile testing to determine the strength of the concrete. We assume that the data are normally distributed, and that the standard deviation calculated for each sample is ?. preferably solve in excel pls help can solve by hand too, thanks

1. Calculate 95% confidence intervals for mix 1 twice; once using the normal distribution and a second time using the t-distribution. Why is the range for the latter larger than the former?
2. Separate modeling studies indicate that the optimal combination must have a compressive strength more than 800 psi.Using the hypothesis testing framework, write null and alternative hypotheses and then test each mix using the t-distribution.Detailed answer please.

Mass (3) Compress (psi) Tensile (psi) 192.3 357 170.5 139.4 314 165.6 139.6 633 193.1 131.4 777 144.1 133.2 163.3 Mass (3) Compress (psi) Tensile (psi) 171.0 667 160.7 177.3 649 159.5 175.2 792 124.1 177.3 673 145.1 176.3 750 Mass (3) Compress (psi) Tensile (psi) 133.3 675 139.2 175.9 733 191.4 175.3 633 131.0 132.0 773 119.3 176.2 690