Question: A civil engineer is choosing 4 materials from a list of 15 to construct a resilient bridge. What is the probability that a specific composite material, known to enhance durability, is among the selected 4? - RTA
What Is the Probability That a Specific Composite Material Appears in a Civil Engineer’s Selection of Four Bridge Materials?
What Is the Probability That a Specific Composite Material Appears in a Civil Engineer’s Selection of Four Bridge Materials?
When planning resilient infrastructure, civil engineers face critical decisions: choosing the right materials from a list—often 15 or more—to ensure durability, safety, and long-term performance. Among the key questions is how likely it is that a high-performance composite material—designed to boost structural resilience—will be included in the final selection. This isn’t just technical trivia; it reflects broader trends in smart construction, risk management, and innovation in public infrastructure. As the U.S. invests heavily in upgrading aging bridges, understanding the role of specific engineered materials becomes essential for stakeholders, planners, and informed citizens alike.
Why This Question Reflects Current Construction Trends
Understanding the Context
With infrastructure modernization gaining momentum across the U.S., the choice of construction materials is undergoing heightened scrutiny. Engineers increasingly prioritize materials that improve longevity, reduce maintenance costs, and withstand extreme weather and heavy loads. In a climate where resilience is no longer optional, selecting the right composite can mean the difference between a bridge that lasts decades and one requiring frequent repairs. This growing focus reflects a shift toward proactive engineering, data-driven material evaluation, and sustainable design—trends amplified by public discourse around climate adaptation and fiscal responsibility.
How the Probability Works: A Clear, Factual Explanation
When an engineer selects 4 materials from a list of 15, every material has an equal chance of being included—assuming a random, unbiased selection process. To find the probability that a specific composite material—say, a high-durability composite—is selected, imagine choosing 4 out of 15: this is a random sample without replacement. The selection depends on chance alone.
To compute the probability that the target material is selected, note it must be among the 4 chosen. For any single material, the chance of being selected is simply:
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Key Insights
Probability = Number of favorable selections / Total possible selections
The total number of ways to choose 4 materials from 15 is given by the combination formula:
C(15, 4) = 15! / (4! × 11!) = 1,365
If the composite material is fixed to be included, the other 3 materials come from the remaining 14. That gives:
C(14, 3) = 14! / (3! × 11!) = 364
Thus, the probability is 364 / 1,365 ≈ 26.7%.
