I29-192

Question

A metropolitan transit authority is considering two plans (Plans A and B) for a new public transportation route. Both plans would provide the same passenger capacity annually. Plan A would use two subway trains, while Plan B would use five buses.
 
Subway trains consume less fuel per passenger transported but generate construction debris that is costly to dispose of. Buses create no such debris.
 
In terms of emissions, trains release about twice as much nitrogen exhaust and more than twice as much particulate matter per passenger as buses.
 
Finally, the two vehicle types differ in noise: each subway train is louder than each bus.Noise is measured in decibels (dB).
 
• Each subway train produces, on average, 90 dB of noise.
 
• Each bus produces, on average, 75 dB of noise.
 
To evaluate overall exposure for the community, the transit authority defines a Noise Exposure Index as:
 
Noise Exposure Index = (average noise per vehicle) × (number of vehicles in the plan)The following table shows the average annual emissions per passenger transported, by vehicle type.
      Vehicle Type   Nitrogen Exhaust (g/passenger)   Particulate Matter (g/passenger)       Train   12   9       Bus   6   4      
Because nitrogen exhaust and particulate matter affect health and the environment in different ways, the transit authority defines two measures:
 
• Pollution Index (PI) = (2 × Nitrogen Exhaust) + (3 × Particulate Matter)
 
• Health Cost Index (HCI) = (0.5 × Nitrogen Exhaust) + (1 × Particulate Matter)
 
To compare overall environmental impact, the authority also defines an Overall Index (OI) as:
 
• Overall Index = (PI + HCI) ÷ 2

Bunuel · Answer

Official Solution:

Noise Exposure Index = (average noise per vehicle) × (number of vehicles in the plan).
 
• Plan A (2 trains): 90 × 2 = 180
 
• Plan B (5 buses): 75 × 5 = 375
 
• Ratio = 375 ÷ 180 = 2.08... ≈ 2

Correct answer:

The ratio of the Noise Exposure Index for Plan B (buses) to that for Plan A (subway trains) is approximately  "2:1"

	1:2
	5:6
	6:5
	3:2
	2:1

	1:2
	5:6
	6:5
	3:2
	2:1

I29-192

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