GMAT Focus Practice Questions — All Questions

After a city installed brighter streetlights on Main Street, traffic accidents there dropped 30% the following year. Officials concluded the new lighting caused the decline. Which statement, if true, most weakens this conclusion?

• a.The new lights cost more to operate than the old ones.
• b.A road closure diverted most through-traffic off Main Street that year, cutting its traffic volume by about 30%.✓
• c.Drivers reported that the brighter lights improved visibility at night.
• d.Accidents on nearby side streets stayed about the same that year.

The conclusion assumes the lighting reduced accidents. If traffic volume itself fell about 30% because of a road closure, then fewer cars, not the lights, could explain the drop, undercutting the causal claim. Cost, driver perceptions, and unchanged side streets do not address whether the lights caused the decline.

Every plant in the greenhouse that received the new fertilizer grew taller than the greenhouse average, so the researcher concluded the fertilizer causes taller growth. This reasoning depends on which assumption?

• a.The fertilizer is inexpensive to produce.
• b.Taller plants always produce more fruit.
• c.The fertilized plants did not also receive some other growth advantage, such as more sunlight, that the unfertilized plants lacked.✓
• d.All plants in the greenhouse are the same species.

A causal conclusion from a comparison requires that the two groups differ only in the suspected cause. If the fertilized plants also got more sunlight or better placement, that alternative could explain their height. The other choices are irrelevant to establishing that the fertilizer, specifically, caused the growth.

A company claims that its new training program improves productivity, citing that employees who completed it produced 15% more than those who did not. Which statement, if true, most strengthens the claim that the program caused the increase?

• a.Before the program, the two groups of employees had produced at nearly identical rates.✓
• b.The program was more expensive than the company expected.
• c.Some employees found the program's schedule inconvenient.
• d.The company plans to expand the program next year.

To support that the program caused the gain, we want evidence the two groups were comparable beforehand. If they produced identically before training, the later 15% gap is better attributed to the program. Cost, scheduling complaints, and future plans say nothing about causation.

All the members of the debate club are also in the honor society. No one in the honor society is a first-year student. Which conclusion follows logically?

• a.Every honor society member is in the debate club.
• b.Some debate club members are first-year students.
• c.Most first-year students join the honor society later.
• d.No member of the debate club is a first-year student.✓

Debate club members are all honor society members, and no honor society member is a first-year student. Therefore no debate club member can be a first-year student. The other options either reverse the first premise or add unsupported claims.