A research facility maintains 72 greenhouse sections.

Question

A research facility maintains 80 greenhouse sections. At four successive inspections, labeled A through D, researchers counted the viable seedlings in every section. Between any two consecutive inspections, the number of viable seedlings in each section either increased, decreased, or remained unchanged.

The table summarizes the changes between consecutive inspections.

Inspection 
interval 
 Sections 
with a gain 
 Average 
gain in seedlings 
 Sections 
with a loss 
 Average 
loss in seedlings 
 Sections 
with no change 
 
  A to B 
 30 
 10 
 40 
 12 
 10 
 
  B to C 
 45 
 12 
 25 
 8 
 10 
 
  C to D 
 42 
 15 
 30 
 10 
 8

For each inspection below, select  Above level at A  if the total number of viable seedlings across all 80 sections was greater at that inspection than at inspection A. Otherwise, select  Not above level at A .

Bunuel · Accepted Answer

Official Solution:

Sections with no change contribute nothing to the increase or decrease in the total number of viable seedlings, so  that column can be ignored when determining  the net change.

For each interval, compare the total gain,

(number of sections with a gain) * (average gain),

with the total loss,

(number of sections with a loss) * (average loss).

• Inspection B

From A to B, fewer sections have a gain than a loss (30 vs. 40), and the average gain is also smaller than the average loss (10 vs. 12).

Thus, the total gain must be smaller than the total loss, so the total number of viable seedlings decreases from A to B.

Answer:  Not above level at A

• Inspection C

From B to C, more sections have a gain than a loss (45 vs. 25), and the average gain is also greater than the average loss (12 vs. 8). Therefore, the total clearly increases from B to C.

To determine whether C is above A, however, we must account for the earlier decrease from A to B.

From A to B:

30 * 10 - 40 * 12
= 300 - 480
= -180

From B to C:

45 * 12 - 25 * 8
= 540 - 200
= 340

Therefore, the cumulative change from A to C is:

-180 + 340 = 160

So the total number of viable seedlings at C is greater than at A.

Answer:  Above level at A

• Inspection D

From C to D, more sections have a gain than a loss (42 vs. 30), and the average gain is also greater than the average loss (15 vs. 10).

Therefore, the total number of viable seedlings increases from C to D.

Since the total at C is already greater than the total at A, and the total increases again from C to D, the total at D must also be greater than the total at A. No further cumulative calculation is needed.

Answer:  Above level at A

Correct answers:

B:  Not above level at A 
C:  Above level at A 
D:  Above level at A

hd29 · Answer

Change in number of seedlings can be calculated by

number of section with gain x avg. Gain - no. of sections with a loss x avg. Loss

So, at point B this no. is -180. So, not above A

at point C this number is +340 adding B. This becomes +160. So above A.

At point D this no. is +330. Adding value at C this effectively becomes +490. So, above A.

A research facility maintains 72 greenhouse sections.

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A research facility maintains 72 greenhouse sections.

Prep Toolkit

615 to 715 in 15 Days (Ria's Strategies)

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745 with Only Self-Prep and GMAT Club

From 555 to 765: 210-point Improvement

Perfect 805 Score Debrief by Julia

My Rewards