Logical ReasoningDifficulty: Medium

PT16 S2 Q9 Explanation

From 1973 to 1989 total energy

A free, expert breakdown of this official LSAT Logical Reasoning question.

TopicsMust be True

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Stimulus

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 goods and services produced in the nation.

What this question is testing

Must be True

Anticipate

Total energy use barely budged (under 10% growth) but electrical use jumped (over 50% growth). When part of a category grows much faster than the whole category, that part takes up a larger share over time.

Evidence

Imagine you owned 100 things, 20 of them blue, in 1973. By 1989 you have under 110 things total, but more than 30 of them are blue. Blue's share went up — even if the total barely grew.

Goal

Find the answer that says electrical energy's share of total energy use went up between 1973 and 1989.

Reading along? Open the full official question in LawHub — we show a fragment here and keep the reasoning in our own words.

The question
9.

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

Answer choices

  1. Too Strong2% picked this

    Most of the energy used in this country in 1989 was

    This claims most energy used in 1989 was electrical. But the stimulus only tells us about percentage changes, not starting levels. Electrical energy could have started as a small fraction of total energy in 1973 and still have grown faster than the total without becoming the majority by 1989. Without baseline data, this conclusion overshoots what the stimulus supports.

  2. Unsupported17% picked this

    From 1973 to 1989 there was a decline in the use of energy other than electrical

    Non-electrical energy use does not have to decline — it just has to grow more slowly than electrical use. Total energy grew, electrical energy grew much faster than total, but non-electrical energy could still have grown slightly (just by less than 10%) while still losing share. The stimulus does not require non-electrical energy use to fall.

  3. Correct71% picked this

    From 1973 to 1989 there was an increase in the proportion of energy use in this country that

    Why this is right

    This must be true. Total energy use grew less than 10%, but electrical energy use grew more than 50%. Whenever a component grows much faster than the whole, that component's share of the whole increases. So the proportion of total energy use that consisted of electrical energy went up between 1973 and 1989.

    Skill tested: Must be True · how this choice captures the argument's function is the move to repeat next time.

  4. Unsupported6% picked this

    In 1989 electrical energy constituted a larger proportion of the energy used to produce the gross national product than did

    The stimulus does not say anything about how each form of energy is used to produce GNP. We know GNP grew, and electrical energy grew, both at similar rates. But we have no information about how much GNP each form of energy supports. This goes beyond what the stimulus tells us.

  5. Unsupported4% picked this

    In 1973 the electrical energy that was produced constituted a smaller proportion of the gross national product than did all

    This compares electrical energy's share of GNP in 1973 to all other forms combined — a comparison the stimulus does not make. We have no information about the relative size of electrical and non-electrical energy in either year, in absolute terms or as shares of GNP.

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