Solved Problems
Problem 1: Variable Classification (Basic)
Classify the following variables by type (Quantitative/Qualitative) and level of measurement.
- The compressive strength of a concrete cylinder (in psi).
- The type of defect in a welded joint (porosity, crack, undercut).
- The rating of a bridge (1 to 10 scale).
- The year a building was constructed.
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Problem 2: Sampling Techniques (Intermediate)
A civil engineering firm wants to study the traffic volume on a particular highway. They decide to measure the number of cars passing a specific point every 15 minutes, starting at 8:00 AM, then 8:15 AM, 8:30 AM, and so on. What type of sampling technique is this?
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Problem 3: Sampling Bias (Advanced Case Study)
A construction company is evaluating the quality of steel rebars delivered by a supplier. An inspector arrives at the site and selects the 10 rebars that are closest to the entrance of the storage yard for tensile strength testing. All 10 rebars pass the test, so the inspector approves the entire delivery of 500 rebars. Identify the sampling method used, potential biases, and recommend a better approach.
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Key Takeaways
- Application: Always identify the data type and collection method before applying statistical techniques.
- Step-by-Step Approach: Follow systematic procedures to solve engineering data analysis problems.
- Sampling Bias: Convenience sampling introduces high risks of bias and should be avoided in critical engineering quality control.