In order to save money, some of Company X's manufacturing plants converted from oil fuel to natural gas last year, when the cost of oil was more than the cost of natural gas. Because of a sudden, unexpected shortage, however, natural gas now costs more than oil, the price of which has fallen steeply over the past year. The cost of conversion back to oil would more than negate any cost savings in fuel. So Company X's fuel costs this year will be significantly higher than they were last year.

Which of the following is an assumption on which the argument above depends?
A. Company X does not have money set aside for the increased costs of fuel.
B. The increase in the cost of fuel cannot be offset by reductions in other operating expenses.
C. The price of natural gas will never again fall below that of oil.
D. The cost of fuel needed by those of Company X's plants that converted to natural gas is not less than the cost of fuel needed by those plants still using oil.
E. The price of oil will not experience a sudden and steep increase.

The correct answer is D.
1. But, if u think logically, even with higher natural gas prices than oil and oil price less than that of last year, the fuel cost of "Company X's plants that converted to natural gas " can be more than the fuel cost of "plants still using oil" and can still have total fuel coat for the company less than last year.

2. Even if we think the oil price stays the same as last year, for the chioce D to be true: the plants should have been divided equally between oil and natural gas as fuel.

Is the question printed wrong? or Please explain , why is choice D correct?

Thanks,

Rajesh

I think you're right, Rajesh! I've passed this along to our curriculum director to take a look - please give him a little time to respond, though, as he's swamped right now.

Thanks for the spot, Rajesh -- we're guilty of poor wording on this question. Unit cost and total cost are not clearly distinguished, for one thing. We'll remove and rehab.

One other thing: I want to point out a generic flaw in your reasoning, Rajesh. Assumptions are NECESSARY but not necessarily SUFFICIENT. When testing an assumption, you should not see whether or not it could lead to an alternative conclusion (as you did). What you should do is NEGATE the assumption and assure yourself that the conclusion CANNOT be correctly drawn then. In other words, the correct assumption will generally NOT get you all the way to the conclusion -- it's just a stepping stone. But if you remove that stepping stone, then you should NOT be able to get to the conclusion. For instance, in this case, you would test D by saying "The cost of fuel needed by those of Company X's plants that converted to natural gas IS less than the cost of fuel needed by those plants still using oil" and then seeing whether you have fatally undermined the conclusion. The way we have written this question, that's not necessarily true (e.g., by changing the *quantities* demanded by the plants in question, you could still make the total cost this year higher than last year's total cost). So be careful with the way you treat assumptions.

Hope that's helpful!!