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Logical Reasoning · Necessary Assumption

PrepTest 102 · Section 3 · Question 13

Phase 1 (your first ~400 questions): read the guidance, then answer. No clock.

Step 1 · Pre-Question Guidance · read this first

Question type
Necessary Assumption
The one idea it tests
Saying 'do it yourself because the helper's deal gives you only a small share' assumes doing it yourself gets you more than that share.
The basic logic
Compare the two options in the argument. The conclusion picks one as better, but the evidence only describes the other. The secret sauce fills in that the chosen option beats the number given.
Tiny words that decide it
  • “only”
  • “Since”
  • “well advised”

Playground logic

Grandpa's burger: the neighbor kid will pick the apples but give Grandpa only one basket out of every ten. Top bun: Grandpa should pick them himself. Secret sauce: picking them himself really gets him more than one basket in ten.

Step 2 · The kid story

Grandpa's Apple Deal

Grandpa's apple tree was loaded. Owen leaned over the fence. "Mr. G, I'll pick every apple for you. Deal is, you get one basket out of every ten. I keep the rest." Grandpa scratched his beard. "One out of ten? That's stingy. I'll pick them myself." Tommy whispered to Priya, "Is that smart?" Priya thought. "Only if Grandpa ends up with more than one basket in ten. His knees are creaky. If he only reaches the low branches, and the rest rot, he might get less." Lulu wrote: The deal being stingy is not enough. Doing it yourself has to beat the deal. Grandpa, hearing this, quietly went to find a ladder. Mr. Whiskers watched from the porch, unimpressed.

Step 3 · Try the model question

Owen offers to pick Grandpa's apples and give him one basket out of every ten. Since that share is so small, Grandpa would do better to pick the apples himself.

Which assumption does the argument need?

Choices

Step 4 · The courtroom tale

The Lost-and-Found Bargain

A school sued a cleaning crew over a deal. The crew had offered: "We will hunt down every lost sweater in the building and give the school back one out of every five we find." The principal refused, saying, "With a share that small, we should search ourselves." Mr. Whitfield, for the crew, smiled. "Your Honor, the school's own search last year found two sweaters out of a hundred. That is far less than one in five." Judge Rowe frowned at the principal. "Your reasoning only works if searching yourselves would get back more than the crew's share. Did you check?" The principal looked at the floor, where, oddly, there was a sweater.

Step 5 · Work the real question

Open PrepTest 102, Section 3, Question 13 in your official copy from LSAC (for example in LawHub) and read it there.

Your answer

How to apply it

Find the two options in the argument and the number attached to one of them. Notice that the conclusion says the other option is better, but no evidence is given about it. Predict the secret sauce: the chosen option must beat that number. Then Pull the Plank on each choice and keep the one whose negation wrecks the comparison. Be wary of choices with different numbers or comparisons the argument never makes.