Free GMAT Multi-Source Reasoning Practice Question (gvx-msr-m4-q3)

An amateur astronomy club received a small grant to image a list of deep-sky targets over one season. Each target can be imaged only on a night that satisfies several constraints at once, and the club must decide which targets are imageable from its site this season. For a target to be imageable on a given night, all of the following must hold:

Altitude: the target must rise at least 30 degrees above the horizon (low targets are blurred by atmosphere). Moon: the night must be a dark night (Moon illumination at most 20 percent) for faint targets; bright targets (magnitude brighter than 6.0) tolerate any Moon. Window: the target's nightly observable window must be at least 90 minutes long to collect enough exposure.

The club images at most one target per usable night and has 24 usable nights this season.

Dark nights available counts how many of the season's usable nights are dark (Moon at most 20 percent) and the target is above 30 degrees during its window. For bright targets (magnitude below 6.0), this column counts all usable nights the target is above 30 degrees, dark or not.

target	peak altitude (degrees)	magnitude	observable window (minutes)	dark nights available
Nebula-A	55 degrees	magnitude 7.4	120 minutes	9 dark nights
Cluster-B	40 degrees	magnitude 5.2	75 minutes	14 dark nights
Galaxy-C	28 degrees	magnitude 8.1	110 minutes	0 dark nights
Nebula-D	62 degrees	magnitude 9.0	95 minutes	6 dark nights
Cluster-E	48 degrees	magnitude 4.8	130 minutes	16 dark nights
Galaxy-F	35 degrees	magnitude 8.8	140 minutes	5 dark nights

A club member is explaining the imaging plan. Assume the gates and magnitude split in the sources. For each of the following statements, select Accurate if it correctly states why the target is or is not handled as described; otherwise select Inaccurate.

Statement 1: Cluster-B is not imageable because its observable window is shorter than the 90-minute minimum, even though its altitude and brightness are fine. Statement 2: Cluster-E is imageable on a bright-Moon night, because its magnitude of 4.8 makes it a bright target that the Moon constraint does not apply to. Statement 3: Galaxy-C is not imageable because it lacks enough dark nights to stack the required exposures.

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Answer & Explanation

Correct answer

1: Accurate · 2: Accurate · 3: Inaccurate

Each statement is graded on whether it names the gate that actually decides the target. Statement 1: Cluster-B has altitude 40 (at least 30) and is bright (magnitude 5.2, so the Moon constraint is waived); the only gate it fails is the window, 75 minutes below the 90-minute minimum. The statement names exactly that gate, so it is Accurate.

Statement 2: Cluster-E has magnitude 4.8, below 6.0, so it is a bright target that ignores the Moon constraint; its altitude 48 and window 130 both clear, so it is imageable on any night including a bright-Moon one. The reasoning is correct, so it is Accurate.

Statement 3: Galaxy-C is indeed not imageable, but the decisive gate is altitude, peak 28 degrees is below 30, and the altitude gate applies to every target before the Moon question is ever reached. Because Galaxy-C never rises above 30 degrees, it has no dark, high-altitude nights at all (its dark-nights count is 0), so the missing dark nights are a downstream consequence of the altitude failure, not the root reason. The statement blames the symptom and skips the gate that actually disqualifies the target, so it is Inaccurate.