Question: Concrete blocks are to be used in the foundations of several buildings. The specifications state that the minimum arithmetic mean compressive strength of a sample of blocks must be 1,000 pounds per square inch (psi). If two companies submit samples of blocks that have mean compressive strengths over the minimum (1,000 psi), then the specifications state that one of two actions will be taken:

i) If a statistical test applied to the sampling results indicate that the samples could have come from the same, or identical, populations, the contract for the blocks will be divided equally.

ii) If the sample statistics indicate that there are two populations involved, the company submitting the blocks having the higher compression will be awarded the contract. The companies involved are Stanblock and Hicompressive.

Stanblock Hicompressive

x bar = 1070 x bar = 1020

n = 81 n = 64

s = 63 s = 57

Following the usual five step hypothesis testing procedures, what would your decision be?

Why would performing this test be important? (Hint – we still may be requiring a t or z test hereJ)