Last year all refuse collected by Shelbyville city services was incinerated. This incineration generated a large quantity of residual ash....
GMAT Critical Reasoning : (CR) Questions
Last year all refuse collected by Shelbyville city services was incinerated. This incineration generated a large quantity of residual ash. In order to reduce the amount of residual ash Shelbyville generates this year to half of last year's total, the city has revamped its collection program. This year city services will separate for recycling enough refuse to reduce the number of truckloads of refuse to be incinerated to half of last year's number.
Which of the following is required for the revamped collection program to achieve its aim?
Passage Analysis:
| Text from Passage | Analysis |
| Last year all refuse collected by Shelbyville city services was incinerated. This incineration generated a large quantity of residual ash. |
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| In order to reduce the amount of residual ash Shelbyville generates this year to half of last year's total, the city has revamped its collection program. |
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| This year city services will separate for recycling enough refuse to reduce the number of truckloads of refuse to be incinerated to half of last year's number. |
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Argument Flow:
The argument starts with a problem (too much ash from burning trash), presents a goal (cut ash in half), and describes a solution (recycle half the trash so only half gets burned). The flow assumes that burning half the truckloads will create half the ash.
Main Conclusion:
Shelbyville's plan to recycle enough refuse to reduce incinerated truckloads by half will achieve their goal of cutting ash production in half.
Logical Structure:
The argument relies on a direct proportional relationship - if we burn half the truckloads, we'll get half the ash. This connection isn't explicitly stated but is the key assumption linking the method (recycling half) to the goal (50% less ash).
Prethinking:
Question type:
Assumption - We need to find what must be true for the plan to work. Think of it as finding the missing link that connects reducing truckloads by half to reducing ash by half.
Precision of Claims
The argument makes very specific quantity claims: exactly half the ash (50% reduction) and exactly half the truckloads (50% reduction). The plan assumes a direct mathematical relationship between these two quantities.
Strategy
For this assumption question, we need to identify what could break the connection between 'half the truckloads' leading to 'half the ash.' We'll look for gaps in the logic - what if the remaining truckloads produce more ash per truckload? What if the recycling process affects ash density? What if the types of refuse change?
'This year, no materials that city services could separate for recycling will be incinerated.' This choice is too extreme. The plan only requires recycling enough materials to cut truckloads in half - it doesn't require that EVERY single recyclable item must be recycled. The city could still accidentally incinerate some recyclable materials and still achieve their goal as long as they hit their target of reducing truckloads by 50%. This goes beyond what's necessary for the plan to work.
'Separating recyclable materials from materials to be incinerated will cost Shelbyville less than half what it cost last year to dispose of the residual ash.' This focuses on cost considerations, but the argument is solely about achieving the physical goal of reducing ash by half. Whether the recycling program is cost-effective compared to ash disposal doesn't affect whether it can achieve the ash reduction target. The plan could work even if it's more expensive.
'Refuse collected by city services will contain a larger proportion of recyclable materials this year than it did last year.' This isn't required because the plan could work even with the same proportion of recyclable materials. If last year had enough recyclable content to support recycling half the refuse, then the same proportion this year would still allow them to recycle enough to cut incinerated truckloads in half. An increase in recyclable proportion would make the plan easier, but it's not necessary.
'The refuse incinerated this year will generate no more residual ash per truckload incinerated than did the refuse incinerated last year.' This is the key assumption. The entire plan relies on the mathematical relationship that burning half the truckloads will produce half the ash. But what if the composition of refuse changes such that the remaining truckloads produce much more ash per truckload? Then 50 truckloads this year could generate just as much ash as 100 truckloads did last year, completely defeating the goal. For the plan to work, we must assume that ash production per truckload doesn't increase. This assumption is absolutely required.
'The total quantity of refuse collected by Shelbyville city service's this year will be no greater than that collected last year.' The plan doesn't depend on the total amount of refuse collected. Even if more refuse is collected this year, as long as they can recycle enough to reduce the incinerated portion to half of last year's truckloads, the plan could still work. The focus is on the absolute number of truckloads sent to incineration, not the proportion of total refuse.