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 compressvie strength of 32.5 Mpa and a standard deviation of 7.5 Mpa and 2nd supplies concrete with a mean compressive strength of 24.5 Mpa and a standard deviation of 3 Mpa.

Assuming normal distribution of test data, the specified compressive strength fc' of 20 Mpa and 95% acceptance probability, determine which manufacturer would meet DOT specs? Negect other considerations.

Explanation / Answer

For DOT project there are two suppliers of ready-mixed concrete. According to QC statistics, the 1st plant provides concrete with a mean compressvie strength of 32.5 Mpa and a standard deviation of 7.5 Mpa and 2nd supplies concrete with a mean compressive strength of 24.5 Mpa and a standard deviation of 3 Mpa.

Assuming normal distribution of test data, the specified compressive strength fc' of 20 Mpa and 95% acceptance probability, determine which manufacturer would meet DOT specs? Negect other considerations.

95% z value =1.96

For the 1st plant,

95% interval = ( 32.5-1.96*7.5, 32.5+1.96*7.5)

=(17.8, 47.2)

For the 2nd plant,

95% interval = ( 24.5-1.96*3, 24.5-1.96*3)

=(18.62, 30.38)

the specified compressive strength fc' of 20 Mpa falls in both manufacturer.

Both manufacturers would met DOT specs.

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