From 1973 to 1989 total energy use in this country increased less than

From 1973 to 1989 total energy use in this country increased less than 10 percent. However, the use of electrical energy in this country during this same period grew by more than 50 percent, as did the gross national product—the total value of all goods and services produced in the nation.

The easiest way to approach this question is to simply use numbers. Let's say Total Energy started at 100, so now we're somewhere below 110. Electrical energy increased by 50%, so it's X+(X*.5). Because we don't know a starting a value relative to the total amount, we should not make any assumptions and just know that it increased by the amount given.

If the statements above are true, then which one of the following must also be true?

(A) Most of the energy used in this country in 1989 was electrical energy. -- Maybe? Sure there is a number, if we assumed above, that could make this true. But there are plenty of numbers that don't. For example, if Electrical was 10 out of 100, and then increased 50%, well now it's 15 out of 110. Out.

(B) From 1973 to 1989 there was a decline in the use of energy other than electrical energy in this country. -- Again, this is a maybe. Could it be true? Sure. But remember that this is not percentage based; this is raw numbers based. So if we go from 100 --> 110 and 99 out 100 (1 for electrical) was the original consumption, we're now at 1.5 for electrical and 108.5 for other. Our consumption went up. Out.

(C) From 1973 to 1989 there was an increase in the proportion of energy use in this country that consisted of electrical energy use. -- This has to be true. Why? Because it increased greater than 50% while the total went up only 10%. Using the 99 - 1 ratio, our electrical use was 1%; as we move to the next set up (108.5 vs 1.5), our proportion goes to about 1.3%. Even if you didn't want to do the math, you could hold this one and eliminate the others before coming back to it.

(D) In 1989 electrical energy constituted a larger proportion of the energy used to produce the gross national product than did any other form of energy. -- We are never told anything about how much energy goes into the GNP, so although this could be true, there is no way this has to be true. Out.

(E) In 1973 the electrical energy that was produced constituted a smaller proportion of the gross national product than did all other forms of energy combined. -- In this scenario, energy is now GNP. But when was this established? Never. All we know is that energy and the GNP increased by 50%, but this doesn't mean that the two are connected. Out.
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OFFICIAL EXPLANATION

We are given the following facts. From 1973 to 1989 total energy use increased less than 10%. During this same period, the use of electrical energy grew by more than 50%. During this same period, the gross national product (GNP) grew by more than 50%. A careful examination of the second sentence reveals that there is no stated connection between the growth of the GNP and the increase in the use of electrical energy. If you assume that the use of electrical energy somehow caused the growth of the GNP, you are guilty of making an unwarranted causal assumption. Because there is no stated connection between the two other than they both grew by more than 50%, any answer that attempts to connect the two is incorrect. Answer choices (D) and (E) can both be eliminated by this reasoning. Now that we recognize that the GNP issue is only a red herring, let us examine the percentages that are given in the stimulus. The 50% increase in electrical energy gives the impression that the jump must have been substantial. But we know from Misconception #6 that a large percentage does not automatically mean a large number. For example, in this problem it is possible that the 50% increase in electrical energy use was a jump from 2 units to 3 units. The possibility that electrical energy use in 1973 was a relatively small percentage of overall energy use directly undermines answer choices (A), as shown by the following example:

1973 1989
Total energy use (in units) 100 109
Electrical energy use 10 15 (in units)
Percentage of total energy use that was electrical 10% 13+%

A close analysis of the chart also reveals that answer choice (B) can be eliminated. In the example, the use of energy other than electrical energy rose from 90 units to 94 units. Although the example disproves both answer choice (A) and (B), obviously you do not have time to make a chart during the test to examine each possibility, so is there a faster way to eliminate the first two answers? Yes—consider the previous discussion point that information about percentages does not tell us about the numbers. With that idea in mind, because the stimulus contains only percentage information (even though there are two percentages), you should be very suspicious of answer choice (A) (which states that the number of electrical units used was greater) and answer choice (B) (which states that the use of non- electrical energy declined) since they both contain numerical information. At the same time, you should be attracted to an answer such as (C) because it contains only percentage information, and as it turns out, answer choice (C) is correct.
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C is the correct answer.Suppose total energy use increased from 100 To 110 from 1973 to 1989.Electrical energy use increased from 5% to 7.5% or 50%.This 50% increase in electrical energy use is accounted by 10% total energy increase from 1973-1989.
Please free to give kudos.

From 1973 to 1989 total energy use in this country increased less than 10 percent. However, the use of electrical energy in this country during this same period grew by more than 50 percent, as did the gross national product—the total value of all goods and services produced in the nation.

If the statements above are true, then which one of the following must also be true?

(A) Most of the energy used in this country in 1989 was electrical energy. - If suppose electrical energy constitured 10% in 1973 and was 15% in 1989 which in 50% increase, still it is not the most used form of energy.

B) From 1973 to 1989 there was a decline in the use of energy other than electrical energy in this country. - If all forms of energy increased like 0.1%, 0.2%
etc and electrical energy increased 50% then this option can also be proved wrong.

(C) From 1973 to 1989 there was an increase in the proportion of energy use in this country that consisted of electrical energy use. - Hold this option, let's not eliminate it, this can be a contender for right answer

(D) In 1989 electrical energy constituted a larger proportion of the energy used to produce the gross national product than did any other form of energy. - same explanation as option A can be given, electrical energy increase by 50% but is overall usage was very less.

(E) In 1973 the electrical energy that was produced constituted a smaller proportion of the gross national product than did all other forms of energy combined. - this option is opposite of option D and can also be proved wrong if we reverse the numbers.

So we are left with option C which is correct.

So ,if the electrical energy usage was highly increased doesn't mean that the energy usage was declined.{In the first statement it was given that energy use was increased in the country less than 10 percent}


SO,OPTION B WAS ELIMINATED
Please correct me if I'm wrong.

(B) From 1973 to 1989 there was a decline in the use of energy other than electrical energy in this country.

total energy use in this country increased less than 10 percent.
Let's say initial value of total energy increase in use was 100E. Then Increase in Total Energy is less than 10E. Total Energy is less than 110E.

the use of electrical energy in this country during this same period grew by more than 50 percent.
Assume electrical Energy was 10% for total energy. This means electrical Energy use was 10E.
50% increase means. electrical Energy use in 1989 became - 15E.
5E increase is coming from electrical energy. What about remaining 4E or 4.5E.
It can be due to increase in other forms of energy. We are not certain here.

And this is must be true question.


Hence we can't conclude that From 1973 to 1989 there was a decline in the use of energy other than electrical energy in this country.

Hope this helps.

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