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# From 1973 to 1989 total energy use in this country increased

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From 1973 to 1989 total energy use in this country increased [#permalink]  24 Mar 2011, 20:05
00:00

Difficulty:

25% (low)

Question Stats:

81% (02:05) correct 18% (01:30) wrong based on 66 sessions
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.
(B) From 1973 to 1989 there was a decline in the use of energy in this country.
(C) From 1973 to 1989 there was an increase in the proportion of energy use in this country that consisted of electrical energy use.
(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.
(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.

I solved it by POE and making math calculations. Is there another faster way to do it?
Source: Powerscore CR
[Reveal] Spoiler: OA

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Re: Electrical energy [#permalink]  25 Mar 2011, 04:08
metallicafan wrote:
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.
We have no information to base this on, we're never told what the initial ratio of electrical to other energy was, nor what the final ratio of electrical to other energy was. We're only told how much each portion increased by itself.

(B) From 1973 to 1989 there was a decline in the use of energy in this country.
This is untrue. Total energy use increased by less than 10 percent, but it still increased.

(C) From 1973 to 1989 there was an increase in the proportion of energy use in this country that consisted of electrical energy use.
Correct. We know that this is true, since electrical use increased more than total energy use.

(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.
Unfounded. Nothing in the statements above indicates what portion of electrical use or energy use went towards production version personal use.

(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.
Again, no information to validate this.
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Re: Electrical energy [#permalink]  25 Mar 2011, 07:58
Thanks jko!
Could you elaborate more choice C, please?
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Re: Electrical energy [#permalink]  25 Mar 2011, 08:17
Sure.

We're told two things which are relevant to C:
1) total energy use increased by 10%
2) electricity use increased by 50%

Consider:
xi/yi = zi

where x = electricity, y = total energy, and z is the portion of total energy that electricity is. i = initial

Now consider what we know about the changes between 1973 and 1989:
1.5xi / 1.1 yi = zf
(1.5/1.1)*(xi/yi) = zf
(1.5/1.1)* zi = zf <-- substituting the equation from 1973

I know you wanted to avoid using math, but it was the easiest way to demonstrate the solution.
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Re: Electrical energy [#permalink]  25 Mar 2011, 10:15
I got the same answer as jko. Pretty straightforward. Less than 10% increase in total energy . Let's say total is 100. It became 109. Let's say electrical energy is 10. It became 25. Hence the ratio 10/100 became 25/109. The proportion of electrial to total increased.

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Re: Electrical energy [#permalink]  25 Mar 2011, 10:47
C is the choice.
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Re: Electrical energy [#permalink]  27 Mar 2011, 18:01
C....
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Re: Electrical energy [#permalink]  02 Sep 2011, 01:06
though C is right but i think E is also right why ?

Less than 10% increase in total energy . Let's say total is 100. It became 109.
now electrical eng use has to be less than 20% of total , in 1973, so as to make total increase less than 10%.

Assume ele eng = 15% of total
rest of energy use , all other forms, = 85%

hence in GNP whatever composition of Total energy use ...electrical eng bound to be less than rest of eng.

can someone plz give me solid reason for E to be wrong.i want my reasoning to be flawed.
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Re: Electrical energy [#permalink]  02 Sep 2011, 02:50
sumitpune wrote:
though C is right but i think E is also right why ?

Less than 10% increase in total energy . Let's say total is 100. It became 109.
now electrical eng use has to be less than 20% of total , in 1973, so as to make total increase less than 10%.

Assume ele eng = 15% of total
rest of energy use , all other forms, = 85%

hence in GNP whatever composition of Total energy use ...electrical eng bound to be less than rest of eng.

can someone plz give me solid reason for E to be wrong.i want my reasoning to be flawed.

I think you misunderstood the answer choice. E says that the contribution of Elec energy towards GNP was lesser than sum of all other forms. But the stimulus gives us no hint of calculating GNP against energy use. It just says that GNP increased as well as the energy use increased. Whereas C actually summarizes the facts from the passage that proportion of total energy use increased, wherein the total energy use consisted of the elec energy. So even if you dont make the calculations in this one it should be fine.
Re: Electrical energy   [#permalink] 02 Sep 2011, 02:50
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# From 1973 to 1989 total energy use in this country increased

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