For DOT project there are two suppliers of ready-mixed concrete. According to QC

Question

For DOT project there are two suppliers of ready-mixed concrete. According to QC statistics, the 1st plant provides concrete with a mean compressive strength of 32.5 MPa and a standard deviation of 7.5 MPa and 2nd supplies concrete with a mean compressive strength of 25.5 MPa and a standard deviation of 2.5 MPa.

Assuming the normal distribution of test data and 95% acceptance probability, determine which manufacturer is of a better value for DOT in terms of compressive strength and reliability? Neglect other considerations.

Question 1 options:

1st, better average strength!

2nd

The same value

Quality is not acceptable for DOT

1st, better average strength!

2nd

The same value

Quality is not acceptable for DOT

Explanation / Answer

I assume you are asking as to which manufacturer is better in terms of compressive strength reliability as to how much they can be relied upon and you are asking as to what can be the range of the 95% confidence interval

That manufacturer is better whose range of the CI is narrower and Q=sigma/mu is lower.

Range=mu+1.96sigma-(mu-1.96sigma)=2*1.96*sigma

First case:Range=29.4MPa , Q=0.23

Second case:Range=9.8MPa , Q=0.098

Hence in any way we see,the 2nd manufacturer is the better.

But maybe if you had given a required value or the range we required,the case may have been different in seeing which values lie in the required range of the manufacturer.

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